Fixed point implementation of range adjustment of components in video coding

ABSTRACT

Processing high dynamic range and or wide color gamut video data using a fixed-point implementation. A method of processing video data may include receiving one or more supplemental enhancement information (SEI) messages that contain information specifying how to determine parameters for performing an inverse dynamic range adjustment process, receiving decoded video data, and performing the inverse dynamic range adjustment process on the decoded video data using fixed-point computing in accordance with the information in the one or more SEI messages.

This application is a continuation of U.S. patent application Ser. No.15/269,558, filed Sep. 19, 2016, which claims the benefit of U.S.Provisional Application No. 62/221,586, filed Sep. 21, 2015, U.S.Provisional Application No. 62/236,804, filed Oct. 2, 2015, and U.S.Provisional Application No. 62/241,063, filed Oct. 13, 2015, the entirecontent of each of which is incorporated by reference herein.

TECHNICAL FIELD

This disclosure relates to video processing.

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, tablet computers, e-book readers, digitalcameras, digital recording devices, digital media players, video gamingdevices, video game consoles, cellular or satellite radio telephones,so-called “smart phones,” video teleconferencing devices, videostreaming devices, and the like. Digital video devices implement videocoding techniques, such as those described in the standards defined byMPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced VideoCoding (AVC), ITU-T H.265, High Efficiency Video Coding (HEVC), andextensions of such standards. The video devices may transmit, receive,encode, decode, and/or store digital video information more efficientlyby implementing such video coding techniques.

Video coding techniques include spatial (intra-picture) predictionand/or temporal (inter-picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (e.g., a video frame or a portion of a video frame) may bepartitioned into video blocks, which may also be referred to astreeblocks, coding units (CUs) and/or coding nodes. Video blocks in anintra-coded (I) slice of a picture are encoded using spatial predictionwith respect to reference samples in neighboring blocks in the samepicture. Video blocks in an inter-coded (P or B) slice of a picture mayuse spatial prediction with respect to reference samples in neighboringblocks in the same picture or temporal prediction with respect toreference samples in other reference pictures. Pictures may be referredto as frames, and reference pictures may be referred to as referenceframes.

Spatial or temporal prediction results in a predictive block for a blockto be coded. Residual data represents pixel differences between theoriginal block to be coded and the predictive block. An inter-codedblock is encoded according to a motion vector that points to a block ofreference samples forming the predictive block, and the residual dataindicating the difference between the coded block and the predictiveblock.

An intra-coded block is encoded according to an intra-coding mode andthe residual data. For further compression, the residual data may betransformed from the pixel domain to a transform domain, resulting inresidual transform coefficients, which then may be quantized. Thequantized transform coefficients, initially arranged in atwo-dimensional array, may be scanned in order to produce aone-dimensional vector of transform coefficients, and entropy coding maybe applied to achieve even more compression.

The total number of color values that may be captured, coded, anddisplayed may be defined by a color gamut. A color gamut refers to therange of colors that a device can capture (e.g., a camera) or reproduce(e.g., a display). Often, color gamuts differ from device to device. Forvideo coding, a predefined color gamut for video data may be used suchthat each device in the video coding process may be configured toprocess pixel values in the same color gamut. Some color gamuts aredefined with a larger range of colors than color gamuts that have beentraditionally used for video coding. Such color gamuts with a largerrange of colors may be referred to as a wide color gamut (WCG).

Another aspect of video data is dynamic range. Dynamic range istypically defined as the ratio between the maximum and minimumbrightness (e.g., luminance) of a video signal. The dynamic range ofcommon video data used in the past is considered to have a standarddynamic range (SDR). Other example specifications for video data definecolor data that has a larger ratio between the maximum and minimumbrightness.

Such video data may be described as having a high dynamic range (HDR).

SUMMARY

This disclosure describes example techniques and devices forimplementing the dynamic range adjustment of components of video datausing a fixed-point implementation. The described techniques areapplicable to video coding standards, not limited to H.264/AVC,H.265/HEVC, and other standards, that are configured to encode anddecode High Dynamic Range (HDR) content.

In one example of the disclosure, a method of processing video datacomprises receiving one or more syntax elements that contain informationspecifying how to determine parameters for performing an inverse dynamicrange adjustment process, receiving decoded video data, and performingthe inverse dynamic range adjustment process on the decoded video datausing fixed-point computing in accordance with the information received.

In another example of the disclosure, an apparatus configured to processvideo data comprises a memory configured to store decoded video data,and one or more processors configured to receive one or more syntaxelements that contain information specifying how to determine parametersfor performing an inverse dynamic range adjustment process, receive thedecoded video data, and perform the inverse dynamic range adjustmentprocess on the decoded video data using fixed-point computing inaccordance with the information received.

In another example of the disclosure, an apparatus configured to processvideo data comprises means for receiving one or more syntax elementsthat contain information specifying how to determine parameters forperforming an inverse dynamic range adjustment process, means forreceiving decoded video data, and means for performing the inversedynamic range adjustment process on the decoded video data usingfixed-point computing in accordance with the information received.

In another example, this disclosure describes a computer-readablestorage medium storing instructions that, when executed, cause one ormore processors of a device configured to process video data to receiveone or more syntax elements that contain information specifying how todetermine parameters for performing an inverse dynamic range adjustmentprocess, receive the decoded video data, and perform the inverse dynamicrange adjustment process on the decoded video data using fixed-pointcomputing in accordance with the information received.

In another example of the disclosure, a method of processing video datacomprises performing a dynamic range adjustment process on video datausing fixed-point computing, and generating one or more syntax elementsthat contain information specifying how to determine parameters forperforming an inverse dynamic range adjustment process, relative to thedynamic range adjustment process, using fixed-point computing.

In another example of the disclosure, an apparatus configured to processvideo data comprises a memory configured to store video data, and one ormore processors configured to perform a dynamic range adjustment processon the video data using fixed-point computing, and generate one or moresyntax elements that contain information specifying how to determineparameters for performing an inverse dynamic range adjustment process,relative to the dynamic range adjustment process, using fixed-pointcomputing.

In another example of the disclosure, an apparatus configured to processvideo data comprises means for performing a dynamic range adjustmentprocess on video data using fixed-point computing, and means forgenerating one or more syntax elements that contain informationspecifying how to determine parameters for performing an inverse dynamicrange adjustment process, relative to the dynamic range adjustmentprocess, using fixed-point computing.

In another example, this disclosure describes a computer-readablestorage medium storing instructions that, when executed, cause one ormore processors of a device configured to process video data to performa dynamic range adjustment process on the video data using fixed-pointcomputing, and generate one or more syntax elements that containinformation specifying how to determine parameters for performing aninverse dynamic range adjustment process, relative to the dynamic rangeadjustment process, using fixed-point computing.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system configured to implement the techniques of thedisclosure.

FIG. 2 is a conceptual drawing showing a typical structure of a colorremapping information (CRI) process.

FIG. 3 is a conceptual drawing illustrating the concepts of HDR data.

FIG. 4 is a conceptual diagram illustrating example color gamuts.

FIG. 5 is a flow diagram illustrating an example of HDR/WCGrepresentation conversion.

FIG. 6 is a flow diagram illustrating an example of HDR/WCG inverseconversion.

FIG. 7 is conceptual diagram illustrating example of Electro-opticaltransfer functions (EOTF) utilized for video data conversion (includingSDR and HDR) from perceptually uniform code levels to linear luminance.

FIG. 8 is a block diagram illustrating an example HDR/WCG conversionapparatus operating according to the techniques of this disclosure.

FIG. 9 is a block diagram illustrating an example HDR/WCG inverseconversion apparatus according to the techniques of this disclosure.

FIG. 10 is a block diagram illustrating an example of a video encoderthat may implement techniques of this disclosure.

FIG. 11 is a block diagram illustrating an example of a video decoderthat may implement techniques of this disclosure.

FIG. 12 is a flowchart showing one example video processing technique ofthe disclosure.

FIG. 13 is a flowchart showing another example video processingtechnique of the disclosure.

DETAILED DESCRIPTION

This disclosure is related to the processing and/or coding of video datawith high dynamic range (HDR) and wide color gamut (WCG)representations. More specifically, the techniques of this disclosureinclude techniques for performing range adjustment of video datacomponents using fixed point processing operations (e.g., as opposed tofloating point processing operations). The techniques and devicesdescribed herein may improve compression efficiency of hybrid-basedvideo coding systems (e.g., H.265/HEVC, H.264/AVC, etc.) utilized forcoding video data, including HDR and WCG video data.

Video coding standards, including hybrid-based video coding standards,include ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-T H.262 or ISO/IECMPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual and ITU-T H.264 (alsoknown as ISO/IEC MPEG-4 AVC), including its Scalable Video Coding (SVC)and Multi-view Video Coding (MVC) extensions. The design of a new videocoding standard, namely High Efficiency Video coding (HEVC, also calledH.265), has been finalized by the Joint Collaboration Team on VideoCoding (JCT-VC) of ITU-T Video Coding Experts Group (VCEG) and ISO/IECMotion Picture Experts Group (MPEG). An HEVC draft specificationreferred to as HEVC Working Draft 10 (WD10), Bross et al., “Highefficiency video coding (HEVC) text specification draft 10 (for FDIS &Last Call),” Joint Collaborative Team on Video Coding (JCT-VC) of ITU-TSG16 WP3 and ISO/IEC JTC1/SC29/WG11, 12th Meeting: Geneva, CH, 14-23Jan. 2013, JCTVC-L1003v34, is available fromhttp://phenix.int-evry.fr/jct/doc_end_user/documents/12_Geneva/wg11/JCTVC-L1003-v34.zip.The finalized HEVC standard is referred to as HEVC version 1.

A defect report, Wang et al., “High efficiency video coding (HEVC)Defect Report,” Joint Collaborative Team on Video Coding (JCT-VC) ofITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG11, 14th Meeting: Vienna, AT, 25July-2 Aug. 2013, JCTVC-N1003v1, is available fromhttp://phenix.int-evry.fr/jct/doc_end_user/documents/14_Vienna/wg11/JCTVC-N1003-v1.zip.The finalized HEVC standard document is published as ITU-T H.265, SeriesH: Audiovisual and Multimedia Systems, Infrastructure of audiovisualservices—Coding of moving video, High efficiency video coding,Telecommunication Standardization Sector of InternationalTelecommunication Union (ITU), April 2013, and another version of thefinalized HEVC standard was published in October 2014. A copy of theH.265/HEVC specification text may be downloaded fromhttp://www.itu.int/rec/T-REC-H.265-201504-I/en.

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system 10 that may utilize techniques of this disclosure. Asshown in FIG. 1, system 10 includes a source device 12 that providesencoded video data to be decoded at a later time by a destination device14. In particular, source device 12 provides the video data todestination device 14 via a computer-readable medium 16. Source device12 and destination device 14 may comprise any of a wide range ofdevices, including desktop computers, notebook (i.e., laptop) computers,tablet computers, set-top boxes, telephone handsets such as so-called“smart” phones, so-called “smart” pads, televisions, cameras, displaydevices, digital media players, video gaming consoles, video streamingdevices, broadcast receiver device, or the like. In some cases, sourcedevice 12 and destination device 14 may be equipped for wirelesscommunication.

Destination device 14 may receive the encoded video data to be decodedvia computer-readable medium 16. Computer-readable medium 16 maycomprise any type of medium or device capable of moving the encodedvideo data from source device 12 to destination device 14. In oneexample, computer-readable medium 16 may comprise a communication mediumto enable source device 12 to transmit encoded video data directly todestination device 14 in real-time. The encoded video data may bemodulated according to a communication standard, such as a wired orwireless communication protocol, and transmitted to destination device14. The communication medium may comprise any wireless or wiredcommunication medium, such as a radio frequency (RF) spectrum or one ormore physical transmission lines. The communication medium may form partof a packet-based network, such as a local area network, a wide-areanetwork, or a global network such as the Internet. The communicationmedium may include routers, switches, base stations, or any otherequipment that may be useful to facilitate communication from sourcedevice 12 to destination device 14.

In other examples, computer-readable medium 16 may includenon-transitory storage media, such as a hard disk, flash drive, compactdisc, digital video disc, Blu-ray disc, or other computer-readablemedia. In some examples, a network server (not shown) may receiveencoded video data from source device 12 and provide the encoded videodata to destination device 14, e.g., via network transmission.Similarly, a computing device of a medium production facility, such as adisc stamping facility, may receive encoded video data from sourcedevice 12 and produce a disc containing the encoded video data.Therefore, computer-readable medium 16 may be understood to include oneor more computer-readable media of various forms, in various examples.

In some examples, encoded data may be output from output interface 22 toa storage device. Similarly, encoded data may be accessed from thestorage device by input interface. The storage device may include any ofa variety of distributed or locally accessed data storage media such asa hard drive, Blu-ray discs, DVDs, CD-ROMs, flash memory, volatile ornon-volatile memory, or any other suitable digital storage media forstoring encoded video data. In a further example, the storage device maycorrespond to a file server or another intermediate storage device thatmay store the encoded video generated by source device 12. Destinationdevice 14 may access stored video data from the storage device viastreaming or download. The file server may be any type of server capableof storing encoded video data and transmitting encoded video data to thedestination device 14. Example file servers include a web server (e.g.,for a website), an FTP server, network attached storage (NAS) devices,or a local disk drive. Destination device 14 may access the encodedvideo data through any standard data connection, including an Internetconnection. This may include a wireless channel (e.g., a Wi-Ficonnection), a wired connection (e.g., DSL, cable modem, etc.), or acombination of both that is suitable for accessing encoded video datastored on a file server. The transmission of encoded video data from thestorage device may be a streaming transmission, a download transmission,or a combination thereof.

The techniques of this disclosure are not necessarily limited towireless applications or settings. The techniques may be applied tovideo coding in support of any of a variety of multimedia applications,such as over-the-air television broadcasts, cable televisiontransmissions, satellite television transmissions, Internet streamingvideo transmissions, such as dynamic adaptive streaming over HTTP(DASH), digital video that is encoded onto a data storage medium,decoding of digital video stored on a data storage medium, or otherapplications. In some examples, system 10 may be configured to supportone-way or two-way video transmission to support applications such asvideo streaming, video playback, video broadcasting, and/or videotelephony.

In the example of FIG. 1, source device 12 includes video source 18,video encoding unit 21, which includes video pre-processor unit 19 andvideo encoder 20, and output interface 22. Destination device 14includes input interface 28, video decoding unit 29, which includesvideo post-processor unit 31 and video decoder 30, and display device32. In accordance with this disclosure, video pre-processor unit 19and/or video encoder 20 of source device 12 and video post-processorunit 31 and/or video decoder 30 of destination device 14 may beconfigured to implement the techniques of this disclosure, includingsignaling and related operations applied to video data in certain colorspaces to enable more efficient compression of HDR and WCG video datawith a fixed point implementation. In some examples, video pre-processorunit 19 may be separate from video encoder 20. In other examples, videopre-processor unit 19 may be part of video encoder 20. Likewise, in someexamples, video post-processor unit 31 may be separate from videodecoder 30. In other examples, video post-processor unit 31 may be partof video decoder 30. In other examples, a source device and adestination device may include other components or arrangements. Forexample, source device 12 may receive video data from an external videosource 18, such as an external camera. Likewise, destination device 14may interface with an external display device, rather than including anintegrated display device.

The illustrated system 10 of FIG. 1 is merely one example. Techniquesfor processing HDR and WCG video data may be performed by any digitalvideo encoding and/or video decoding device. Moreover, the techniques ofthis disclosure may also be performed by a video pre-processor and/orvideo post-processor (e.g., video pre-processor unit 19 and videopost-processor unit 31). In general, a video pre-processor may be anydevice configured to process video data before encoding (e.g., beforeHEVC encoding). In general, a video post-processor may be any deviceconfigured to process video data after decoding (e.g., after HEVCdecoding). Source device 12 and destination device 14 are merelyexamples of such coding devices in which source device 12 generatescoded video data for transmission to destination device 14. In someexamples, devices 12, 14 may operate in a substantially symmetricalmanner such that each of devices 12, 14 include video encoding anddecoding components, as well as a video pre-processor and a videopost-processor (e.g., video pre-processor unit 19 and videopost-processor unit 31, respectively). Hence, system 10 may supportone-way or two-way video transmission between video devices 12, 14,e.g., for video streaming, video playback, video broadcasting, or videotelephony.

Video source 18 of source device 12 may include a video capture device,such as a video camera, a video archive containing previously capturedvideo, and/or a video feed interface to receive video from a videocontent provider. As a further alternative, video source 18 may generatecomputer graphics-based data as the source video, or a combination oflive video, archived video, and computer-generated video. In some cases,if video source 18 is a video camera, source device 12 and destinationdevice 14 may form so-called camera phones or video phones. As mentionedabove, however, the techniques described in this disclosure may beapplicable to video coding and video processing, in general, and may beapplied to wireless and/or wired applications. In each case, thecaptured, pre-captured, or computer-generated video may be encoded byvideo encoding unit 21. The encoded video information may then be outputby output interface 22 onto a computer-readable medium 16.

Input interface 28 of destination device 14 receives information fromcomputer-readable medium 16. The information of computer-readable medium16 may include syntax information defined by video encoder 20, which isalso used by video decoding unit 29, that includes syntax elements thatdescribe characteristics and/or processing of blocks and other codedunits, e.g., groups of pictures (GOPs). Display device 32 displays thedecoded video data to a user, and may comprise any of a variety ofdisplay devices such as a cathode ray tube (CRT), a liquid crystaldisplay (LCD), a plasma display, an organic light emitting diode (OLED)display, or another type of display device.

As illustrated, video pre-processor unit 19 receives the video data fromvideo source 18. Video pre-processor unit 19 may be configured toprocess the video data to convert it into a form that is suitable forencoding with video encoder 20. For example, video pre-processor unit 19may perform dynamic range compacting (e.g., using a non-linear transferfunction), color conversion to a more compact or robust color space,and/or floating-to-integer representation conversion. Video encoder 20may perform video encoding on the video data outputted by videopre-processor unit 19. Video decoder 30 may perform the inverse of videoencoder 20 to decode video data, and video post-processor unit 31 mayperform the inverse of video pre-processor unit 19 to convert the videodata into a form suitable for display. For instance, videopost-processor unit 31 may perform integer-to-floating conversion, colorconversion from the compact or robust color space, and/or the inverse ofthe dynamic range compacting to generate video data suitable fordisplay.

Video encoder 20 and video decoder 30 each may be implemented as any ofa variety of suitable encoder circuitry, such as one or moremicroprocessors, digital signal processors (DSPs), application specificintegrated circuits (ASICs), field programmable gate arrays (FPGAs),discrete logic, software, hardware, firmware or any combinationsthereof. When the techniques are implemented partially in software, adevice may store instructions for the software in a suitable,non-transitory computer-readable medium and execute the instructions inhardware using one or more processors to perform the techniques of thisdisclosure. Each of video encoder 20 and video decoder 30 may beincluded in one or more encoders or decoders, either of which may beintegrated as part of a combined encoder/decoder (CODEC) in a respectivedevice.

Video pre-processor unit 19 and video post-processor unit 31 each may beimplemented as any of a variety of suitable encoder circuitry, such asone or more microprocessors, digital signal processors (DSPs),application specific integrated circuits (ASICs), field programmablegate arrays (FPGAs), discrete logic, software, hardware, firmware or anycombinations thereof. When the techniques are implemented partially insoftware, a device may store instructions for the software in asuitable, non-transitory computer-readable medium and execute theinstructions in hardware using one or more processors to perform thetechniques of this disclosure. As discussed above video pre-processorunit 19 and video post-processor unit 31 be separate devices from videoencoder 20 and video decoder 30, respectively. In other examples, videopre-processor unit 19 may integrate with video encoder 20 in a singledevice and inverse video post-processor unit 31 may be integrated withvideo decoder 30 in a single device.

In some examples, video encoder 20 and video decoder 30 operateaccording to a video compression standard, such as ISO/IEC MPEG-4 Visualand ITU-T H.264 (also known as ISO/IEC MPEG-4 AVC), including itsScalable Video Coding (SVC) extension, Multi-view Video Coding (MVC)extension, and MVC-based three-dimensional video (3DV) extension. Insome instances, any bitstream conforming to MVC-based 3DV alwayscontains a sub-bitstream that is compliant to a MVC profile, e.g.,stereo high profile. Furthermore, there is an ongoing effort to generatea 3DV coding extension to H.264/AVC, namely AVC-based 3DV. Otherexamples of video coding standards include ITU-T H.261, ISO/IEC MPEG-1Visual, ITU-T H.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IECMPEG-4 Visual, and ITU-T H.264, ISO/IEC Visual. In other examples, videoencoder 20 and video decoder 30 may be configured to operate accordingto the HEVC standard.

In HEVC and other video coding standards, a video sequence typicallyincludes a series of pictures. Pictures may also be referred to as“frames.” A picture may include three sample arrays, denoted S_(L),S_(Cb), and S_(Cr). S_(L) is a two-dimensional array (i.e., a block) ofluma samples. S_(Cb) is a two-dimensional array of Cb chrominancesamples. S_(Cr) is a two-dimensional array of Cr chrominance samples.Chrominance samples may also be referred to herein as “chroma” samples.In other instances, a picture may be monochrome and may only include anarray of luma samples.

Video encoder 20 may generate a set of coding tree units (CTUs). Each ofthe CTUs may comprise a coding tree block of luma samples, twocorresponding coding tree blocks of chroma samples, and syntaxstructures used to code the samples of the coding tree blocks. In amonochrome picture or a picture that has three separate color planes, aCTU may comprise a single coding tree block and syntax structures usedto code the samples of the coding tree block. A coding tree block may bean N×N block of samples. A CTU may also be referred to as a “tree block”or a “largest coding unit” (LCU). The CTUs of HEVC may be broadlyanalogous to the macroblocks of other video coding standards, such asH.264/AVC. However, a CTU is not necessarily limited to a particularsize and may include one or more coding units (CUs). A slice may includean integer number of CTUs ordered consecutively in the raster scan.

This disclosure may use the term “video unit” or “video block” to referto one or more blocks of samples and syntax structures used to codesamples of the one or more blocks of samples. Example types of videounits may include CTUs, CUs, PUs, transform units (TUs) in HEVC, ormacroblocks, macroblock partitions, and so on in other video codingstandards.

To generate a coded CTU, video encoder 20 may recursively performquad-tree partitioning on the coding tree blocks of a CTU to divide thecoding tree blocks into coding blocks, hence the name “coding treeunits.” A coding block is an N×N block of samples. A CU may comprise acoding block of luma samples and two corresponding coding blocks ofchroma samples of a picture that has a luma sample array, a Cb samplearray and a Cr sample array, and syntax structures used to code thesamples of the coding blocks. In a monochrome picture or a picture thathas three separate color planes, a CU may comprise a single coding blockand syntax structures used to code the samples of the coding block.

Video encoder 20 may partition a coding block of a CU into one or moreprediction blocks. A prediction block may be a rectangular (i.e., squareor non-square) block of samples on which the same prediction is applied.A prediction unit (PU) of a CU may comprise a prediction block of lumasamples, two corresponding prediction blocks of chroma samples of apicture, and syntax structures used to predict the prediction blocksamples. In a monochrome picture or a picture that have three separatecolor planes, a PU may comprise a single prediction block and syntaxstructures used to predict the prediction block samples. Video encoder20 may generate predictive luma, Cb and Cr blocks for luma, Cb and Crprediction blocks of each PU of the CU.

Video encoder 20 may use intra prediction or inter prediction togenerate the predictive blocks for a PU. If video encoder 20 uses intraprediction to generate the predictive blocks of a PU, video encoder 20may generate the predictive blocks of the PU based on decoded samples ofthe picture associated with the PU.

If video encoder 20 uses inter prediction to generate the predictiveblocks of a PU, video encoder 20 may generate the predictive blocks ofthe PU based on decoded samples of one or more pictures other than thepicture associated with the PU. Inter prediction may be uni-directionalinter prediction (i.e., uni-prediction) or bi-directional interprediction (i.e., bi-prediction). To perform uni-prediction orbi-prediction, video encoder 20 may generate a first reference picturelist (RefPicList0) and a second reference picture list (RefPicList1) fora current slice.

Each of the reference picture lists may include one or more referencepictures.

When using uni-prediction, video encoder 20 may search the referencepictures in either or both RefPicList0 and RefPicList1 to determine areference location within a reference picture. Furthermore, when usinguni-prediction, video encoder 20 may generate, based at least in part onsamples corresponding to the reference location, the predictive sampleblocks for the PU. Moreover, when using uni-prediction, video encoder 20may generate a single motion vector that indicates a spatialdisplacement between a prediction block of the PU and the referencelocation. To indicate the spatial displacement between a predictionblock of the PU and the reference location, a motion vector may includea horizontal component specifying a horizontal displacement between theprediction block of the PU and the reference location and may include avertical component specifying a vertical displacement between theprediction block of the PU and the reference location.

When using bi-prediction to encode a PU, video encoder 20 may determinea first reference location in a reference picture in RefPicList0 and asecond reference location in a reference picture in RefPicList1. Videoencoder 20 may then generate, based at least in part on samplescorresponding to the first and second reference locations, thepredictive blocks for the PU. Moreover, when using bi-prediction toencode the PU, video encoder 20 may generate a first motion indicating aspatial displacement between a sample block of the PU and the firstreference location and a second motion indicating a spatial displacementbetween the prediction block of the PU and the second referencelocation.

After video encoder 20 generates predictive luma, Cb, and Cr blocks forone or more PUs of a CU, video encoder 20 may generate a luma residualblock for the CU. Each sample in the CU's luma residual block indicatesa difference between a luma sample in one of the CU's predictive lumablocks and a corresponding sample in the CU's original luma codingblock. In addition, video encoder 20 may generate a Cb residual blockfor the CU. Each sample in the CU's Cb residual block may indicate adifference between a Cb sample in one of the CU's predictive Cb blocksand a corresponding sample in the CU's original Cb coding block. Videoencoder 20 may also generate a Cr residual block for the CU. Each samplein the CU's Cr residual block may indicate a difference between a Crsample in one of the CU's predictive Cr blocks and a correspondingsample in the CU's original Cr coding block.

Furthermore, video encoder 20 may use quad-tree partitioning todecompose the luma, Cb and, Cr residual blocks of a CU into one or moreluma, Cb, and Cr transform blocks. A transform block may be arectangular block of samples on which the same transform is applied. Atransform unit (TU) of a CU may comprise a transform block of lumasamples, two corresponding transform blocks of chroma samples, andsyntax structures used to transform the transform block samples. In amonochrome picture or a picture that has three separate color planes, aTU may comprise a single transform block and syntax structures used totransform the transform block samples. Thus, each TU of a CU may beassociated with a luma transform block, a Cb transform block, and a Crtransform block. The luma transform block associated with the TU may bea sub-block of the CU's luma residual block. The Cb transform block maybe a sub-block of the CU's Cb residual block. The Cr transform block maybe a sub-block of the CU's Cr residual block.

Video encoder 20 may apply one or more transforms to a luma transformblock of a TU to generate a luma coefficient block for the TU. Acoefficient block may be a two-dimensional array of transformcoefficients. A transform coefficient may be a scalar quantity. Videoencoder 20 may apply one or more transforms to a Cb transform block of aTU to generate a Cb coefficient block for the TU. Video encoder 20 mayapply one or more transforms to a Cr transform block of a TU to generatea Cr coefficient block for the TU.

After generating a coefficient block (e.g., a luma coefficient block, aCb coefficient block or a Cr coefficient block), video encoder 20 mayquantize the coefficient block. Quantization generally refers to aprocess in which transform coefficients are quantized to possibly reducethe amount of data used to represent the transform coefficients,providing further compression. Furthermore, video encoder 20 may inversequantize transform coefficients and apply an inverse transform to thetransform coefficients in order to reconstruct transform blocks of TUsof CUs of a picture. Video encoder 20 may use the reconstructedtransform blocks of TUs of a CU and the predictive blocks of PUs of theCU to reconstruct coding blocks of the CU. By reconstructing the codingblocks of each CU of a picture, video encoder 20 may reconstruct thepicture. Video encoder 20 may store reconstructed pictures in a decodedpicture buffer (DPB). Video encoder 20 may use reconstructed pictures inthe DPB for inter prediction and intra prediction.

After video encoder 20 quantizes a coefficient block, video encoder 20may entropy encode syntax elements that indicate the quantized transformcoefficients. For example, video encoder 20 may perform Context-AdaptiveBinary Arithmetic Coding (CABAC) on the syntax elements indicating thequantized transform coefficients. Video encoder 20 may output theentropy-encoded syntax elements in a bitstream.

Video encoder 20 may output a bitstream that includes a sequence of bitsthat forms a representation of coded pictures and associated data. Thebitstream may comprise a sequence of network abstraction layer (NAL)units. Each of the NAL units includes a NAL unit header and encapsulatesa raw byte sequence payload (RBSP). The NAL unit header may include asyntax element that indicates a NAL unit type code. The NAL unit typecode specified by the NAL unit header of a NAL unit indicates the typeof the NAL unit. A RBSP may be a syntax structure containing an integernumber of bytes that is encapsulated within a NAL unit. In someinstances, an RBSP includes zero bits.

Different types of NAL units may encapsulate different types of RBSPs.For example, a first type of NAL unit may encapsulate a RBSP for apicture parameter set (PPS), a second type of NAL unit may encapsulate aRBSP for a coded slice, a third type of NAL unit may encapsulate a RBSPfor Supplemental Enhancement Information (SEI), and so on. A PPS is asyntax structure that may contain syntax elements that apply to zero ormore entire coded pictures. NAL units that encapsulate RBSPs for videocoding data (as opposed to RBSPs for parameter sets and SEI messages)may be referred to as video coding layer (VCL) NAL units. A NAL unitthat encapsulates a coded slice may be referred to herein as a codedslice NAL unit. A RBSP for a coded slice may include a slice header andslice data.

Video decoder 30 may receive a bitstream. In addition, video decoder 30may parse the bitstream to decode syntax elements from the bitstream.Video decoder 30 may reconstruct the pictures of the video data based atleast in part on the syntax elements decoded from the bitstream. Theprocess to reconstruct the video data may be generally reciprocal to theprocess performed by video encoder 20. For instance, video decoder 30may use motion vectors of PUs to determine predictive blocks for the PUsof a current CU. Video decoder 30 may use a motion vector or motionvectors of PUs to generate predictive blocks for the PUs.

In addition, video decoder 30 may inverse quantize coefficient blocksassociated with TUs of the current CU. Video decoder 30 may performinverse transforms on the coefficient blocks to reconstruct transformblocks associated with the TUs of the current CU. Video decoder 30 mayreconstruct the coding blocks of the current CU by adding the samples ofthe predictive sample blocks for PUs of the current CU to correspondingsamples of the transform blocks of the TUs of the current CU. Byreconstructing the coding blocks for each CU of a picture, video decoder30 may reconstruct the picture. Video decoder 30 may store decodedpictures in a decoded picture buffer for output and/or for use indecoding other pictures.

Supplemental Enhancement information (SEI) messages are often includedin video bitstreams, typically to carry information that is notessential in order to decode the bitstream by the decoder (e.g., videodecoder 30). The information contained in an SEI message may be usefulin improving the display or processing of the decoded output; e.g. suchinformation could be used by decoder-side entities to improve theviewability of the content. It is also possible that certain applicationstandards could mandate the presence of such SEI messages in thebitstream so that the improvement in quality can be brought to alldevices that conform to the application standard (e.g., the carriage ofthe frame-packing SEI message for frame-compatible plano-stereoscopic3DTV video format, where the SEI message is carried for every frame ofthe video, e.g., as described in ETSI—TS 101 547-2, Digital VideoBroadcasting (DVB) Plano-stereoscopic 3DTV; Part 2: Frame compatibleplano-stereoscopic 3DTV, handling of recovery point SEI message, e.g.,as described in 3GPP TS 26.114 v13.0.0, 3rd Generation PartnershipProject; Technical Specification Group Services and System Aspects; IPMultimedia Subsystem (IMS); Multimedia Telephony; Media handling andinteraction (Release 13), or use of pan-scan scan rectangle SEI messagein DVB, e.g., as described in ETSI—TS 101 154, Digital VideoBroadcasting (DVB); Specification for the use of Video and Audio Codingin Broadcasting Applications based on the MPEG-2 Transport Stream).

A tone-mapping information SEI message is used to map luma samples, oreach of RGB component samples. Different values of tone_map_id are usedto define different purposes, and the syntax of the tone-map SEI messageis also modified accordingly. A value of 1 for the tone_map_id allowsthe SEI message to clip the RGB samples to a minimum and a maximumvalue. A value of 3 for the tone_map_id allows the signaling of a lookup table in the form of pivot points. However, when applied, the samevalues are applied to all RGB components, or only applied to the lumacomponent.

A knee function SEI message is used to indicate the mapping of the RGBcomponents of the decoded pictures in the normalized linear domain. Theinput and output maximum luminance values are also indicated, and alook-up table maps the input luminance values to the output luminancevalues. The same look-up table is applied to all the three colorcomponents.

A color remapping information (CRI) SEI message defined in the HEVCstandard is used to convey information that is used to map pictures inone color space to another. In one example, the syntax of the CRI SEImessage includes three parts—first look-up table (Pre-LUT), followed bya 3×3 matrix indicating color remapping coefficients, followed by asecond look-up table (Post-LUT). For each color component, e.g., R,G,Bor Y,Cb,Cr, independent LUT is defined for both, Pre-LUT and Post-LUT.The CRI SEI message also includes syntax element called colour_remap_id,different values of which may be used to indicate different purposes ofthe SEI message. FIG. 2 shows a typical structure of the color remappinginformation process specified by a CRI SEI message.

Dynamic range adjustment (DRA) SEI message. The dynamic range adjustmentSEI message, e.g., as described in D. Bugdayci Sansli, A. K.Ramasubramonian, D. Rusanovskyy, S. Lee, J. Sole, M. Karczewicz, Dynamicrange adjustment SEI message, m36330, MPEG meeting, Warsaw, Poland,22-26 June, 2015, has not been adopted as part of any video codingstandard; however, the SEI message includes signaling of one set ofscale and offset numbers to map the input samples. The SEI message alsoallows the signaling of different look-up tables for differentcomponents, and also allows for signaling optimization when the samescale and offset are to be used for more than one component. The scaleand offset numbers are signaled in fixed length accuracy.

Next generation video applications are anticipated to operate with videodata representing captured scenery with HDR and a WCG. Parameters of theutilized dynamic range and color gamut are two independent attributes ofvideo content, and their specification for purposes of digitaltelevision and multimedia services are defined by several internationalstandards. For example, ITU-R Rec. BT.709, “Parameter values for theHDTV standards for production and international programme exchange,” andITU-R Rec. BT.2020, “Parameter values for ultra-high definitiontelevision systems for production and international programme exchange,”defines parameters for HDTV (high definition television) and UHDTV(ultra-high definition television), respectively, such as standarddynamic range (SDR) and color primaries that extend beyond the standardcolor gamut. Rec. BT.2100, “Image parameter values for high dynamicrange television for use in production and international programmeexchange” defines transfer functions and representations for HDRtelevision use, including primaries that support wide color gamutrepresentations. There are also other standards developing organization(SDOs) documents that specify dynamic range and color gamut attributesin other systems, e.g., DCI-P3 color gamut is defined in SMPTE-231-2(Society of Motion Picture and Television Engineers) and some parametersof HDR are defined in SMPTE-2084. A brief description of dynamic rangeand color gamut for video data is provided below.

Dynamic range is typically defined as the ratio between the maximum andminimum brightness (e.g., luminance) of the video signal. Dynamic rangemay also be measured in terms of ‘f-stop,’ where one f-stop correspondsto a doubling of a signal's dynamic range. In MPEG's definition, contentthat features brightness variation with more than 16 f-stops is referredas HDR content. In some terms, levels between 10 and 16 f-stops areconsidered as intermediate dynamic range, but it is considered HDR inother definitions. In some examples of this disclosure, HDR videocontent may be any video content that has a higher dynamic range thantraditionally used video content with a standard dynamic range (e.g.,video content as specified by ITU-R Rec. BT.709).

The human visual system (HVS) is capable for perceiving much largerdynamic ranges than SDR content and HDR content. However, the HVSincludes an adaptation mechanism to narrow the dynamic range of the HVSto a so-called simultaneous range. The width of the simultaneous rangemay be dependent on current lighting conditions (e.g., currentbrightness). Visualization of dynamic range provided by SDR of HDTV,expected HDR of UHDTV and HVS dynamic range is shown in FIG. 3, althoughthe exact range may vary based on each individual and display.

Current video application and services are regulated by ITU Rec.709 andprovide SDR, typically supporting a range of brightness (e.g.,luminance) of around 0.1 to 100 candelas (cd) per m2 (often referred toas “nits”), leading to less than 10 f-stops. Some example nextgeneration video services are expected to provide dynamic range of up to16 f-stops. Although detailed specifications for such content arecurrently under development, some initial parameters have been specifiedin SMPTE-2084 and ITU-R Rec. 2020.

Another aspect for a more realistic video experience, besides HDR, isthe color dimension. Color dimension is typically defined by the colorgamut. FIG. 4 is a conceptual diagram showing an SDR color gamut(triangle 100 based on the BT.709 color primaries), and the wider colorgamut that for UHDTV (triangle 102 based on the BT.2020 colorprimaries). FIG. 4 also depicts the so-called spectrum locus (delimitedby the tongue-shaped area 104), representing the limits of the naturalcolors. As illustrated by FIG. 3, moving from BT.709 (triangle 100) toBT.2020 (triangle 102) color primaries aims to provide UHDTV serviceswith about 70% more colors. D65 specifies an example white color for theBT.709 and/or BT.2020 specifications.

Examples of color gamut specifications for the DCI-P3, BT.709, andBT.2020 color spaces are shown in Table 1.

TABLE 1 Color gamut parameters RGB color space parameters Color Whitepoint Primary colors space xx_(W) yy_(W) xx_(R) yy_(R) xx_(G) yy_(G)xx_(B) yy_(B) DCI-P3 0.314 0.351 0.680 0.320 0.265 0.690 0.150 0.060ITU-R 0.3127 0.3290 0.64 0.33 0.30 0.60 0.15 0.06 BT.709 ITU-R 0.31270.3290 0.708 0.292 0.170 0.797 0.131 0.046 BT.2020

As can be seen in Table 1, a color gamut may be defined by the X and Yvalues of a white point, and by the x and y values of the primary colors(e.g., red (R), green (G), and blue (B). The x and y values representnormalized values that are derived from the chromaticity (X and Z) andthe brightness (Y) of the colors, as is defined by the CIE 1931 colorspace. The CIE 1931 color space defines the links between pure colors(e.g., in terms of wavelengths) and how the human eye perceives suchcolors.

HDR/WCG video data is typically acquired and stored at a very highprecision per component (even floating point), with the 4:4:4 chromaformat and a very wide color space (e.g., CIE XYZ). This representationtargets high precision and is almost mathematically lossless. However,such a format for storing HDR/WCG video data may include a lot ofredundancies and may not be optimal for compression purposes. A lowerprecision format with HVS-based assumptions is typically utilized forstate-of-the-art video applications.

One example of a video data format conversion process for purposes ofcompression includes three major processes, as shown in FIG. 5. Thetechniques of FIG. 5 may be performed by source device 12. Linear RGBdata 110 may be HDR/WCG video data and may be stored in a floating pointrepresentation. Linear RGB data 110 may be compacted using a non-lineartransfer function (TF) 112 for dynamic range compacting. Transferfunction 112 may compact linear RGB data 110 using any number ofnon-linear transfer functions, e.g., the PQ TF as defined in SMPTE-2084.In some examples, color conversion process 114 converts the compacteddata into a more compact or robust color space (e.g., a YUV or YCrCbcolor space) that is more suitable for compression by a hybrid videoencoder. This data is then quantized using a floating-to-integerrepresentation quantization unit 116 to produce converted HDR′ data 118.In this example HDR′ data 118 is in an integer representation. The HDR′data is now in a format more suitable for compression by a hybrid videoencoder (e.g., video encoder 20 applying HEVC techniques). The order ofthe processes depicted in FIG. 5 is given as an example, and may vary inother applications. For example, color conversion may precede the TFprocess. In addition, additional processing, e.g. spatial subsampling,may be applied to color components.

The inverse conversion at the decoder side is depicted in FIG. 6. Thetechniques of FIG. 6 may be performed by destination device 14.Converted HDR′ data 120 may be obtained at destination device 14 throughdecoding video data using a hybrid video decoder (e.g., video decoder 30applying HEVC techniques). HDR′ data 120 may then be inverse quantizedby inverse quantization unit 122. Then an inverse color conversionprocess 124 may be applied to the inverse quantized HDR′ data. Theinverse color conversion process 124 may be the inverse of colorconversion process 114. For example, the inverse color conversionprocess 124 may convert the HDR′ data from a YCrCb format back to an RGBformat. Next, inverse transfer function 126 may be applied to the datato add back the dynamic range that was compacted by transfer function112 to recreate the linear RGB data 128.

The techniques depicted in FIG. 5 will now be discussed in more detail.In general, a transfer function is applied to data (e.g., HDR/WCG videodata) to compact the dynamic range of the data such that errors due toquantization are perceptually uniform (approximately) across the rangeof luminance values. Such compaction allows the data to be representedwith fewer bits. In one example, the transfer function may be aone-dimensional (1D) non-linear function and may reflect the inverse ofan electro-optical transfer function (EOTF) of the end-user display,e.g., as specified for SDR in Rec. 709. In another example, the transferfunction may approximate the HVS perception to brightness changes, e.g.,the PQ transfer function specified in SMPTE-2084 for HDR. The inverseprocess of the OETF is the EOTF (electro-optical transfer function),which maps the code levels back to luminance. FIG. 7 shows severalexamples of non-linear transfer function used as EOTFs. The transferfunctions may also be applied to each R, G and B component separately.

In the context of this disclosure, the terms “signal value” or “colorvalue” may be used to describe a luminance level corresponding to thevalue of a specific color component (such as R, G, B, or Y) for an imageelement. The signal value is typically representative of a linear lightlevel (luminance value). The terms “code level” or “digital code value”may refer to a digital representation of an image signal value.Typically, such a digital representation is representative of anonlinear signal value. An EOTF represents the relationship between thenonlinear signal values provided to a display device (e.g., displaydevice 32) and the linear color values produced by the display device.

RGB data is typically utilized as the input color space, since RGB isthe type of data that is typically produced by image-capturing sensors.However, the RGB color space has high redundancy among its componentsand is not optimal for compact representation. To achieve more compactand a more robust representation, RGB components are typically converted(e.g., a color transform is performed) to a more uncorrelated colorspace that is more suitable for compression, e.g., YCbCr. A YCbCr colorspace separates the brightness in the form of luminance (Y) and colorinformation (CrCb) in different less correlated components. In thiscontext, a robust representation may refer to a color space featuringhigher levels of error resilience when compressed at a constrainedbitrate.

Following the color transform, input data in a target color space may bestill represented at high bit-depth (e.g. floating point accuracy). Thehigh bit-depth data may be converted to a target bit-depth, for example,using a quantization process. Certain studies show that 10-12 bitsaccuracy in combination with the PQ transfer is sufficient to provideHDR data of 16 f-stops with distortion below the Just-NoticeableDifference (JND). In general, a JND is the amount of something (e.g.,video data) must be change in order for a difference to be noticeable(e.g., by the HVS). Data represented with 10-bit accuracy can be furthercoded with most of the state-of-the-art video coding solutions. Thisquantization is an element of lossy coding and is a source of inaccuracyintroduced to converted data.

It is anticipated that next generation HDR/WCG video applications willoperate with video data captured at different parameters of HDR and CG.Examples of different configuration can be the capture of HDR videocontent with peak brightness up-to 1000 nits, or up-to 10,000 nits.Examples of different color gamuts may include BT.709, BT.2020 as wellSMPTE specified-P3, or others.

It is also anticipated that a single color space, e.g., a target colorcontainer, that incorporates (or nearly incorporates) all othercurrently used color gamuts to be utilized in future. One example ofsuch a target color container is BT.2020. Support of a single targetcolor container would significantly simplify standardization,implementation and deployment of HDR/WCG systems, since a reduced numberof operational points (e.g., number of color containers, color spaces,color conversion algorithms, etc.) and/or a reduced number of requiredalgorithms should be supported by a decoder (e.g., video decoder 30).

In one example of such a system, content captured with a native colorgamut (e.g. P3 or BT.709) different from the target color container(e.g. BT.2020) may be converted to the target container prior toprocessing (e.g., prior to video encoding).

Below are several examples of such conversion:

RGB conversion from BT.709 to BT.2020 color container:

R ₂₀₂₀=0.627404078626*R ₇₀₉+0.329282097415*G ₇₀₉+0.043313797587*B ₇₀₉

G ₂₀₂₀=0.069097233123*R ₇₀₉+0.919541035593*G ₇₀₉+0.011361189924*B ₇₀₉

B ₂₀₂₀=0.016391587664*R ₇₀₉+0.088013255546*G ₇₀₉+0.895595009604*B ₇₀₉  (1)

RGB conversion from P3 to BT.2020 color container:

R ₂₀₂₀=0.753832826496*R _(P3)+0.198597635641*G _(P3)+0.047569409186*B_(P3)

G ₂₀₂₀=0.045744636411*R _(P3)+0.941777687331*G _(P3)+0.012478735611*B_(P3)

B ₂₀₂₀=−0.001210377285*R _(P3)+0.017601107390*G _(P3)+0.983608137835*B_(P3)   (2)

During this conversion, the value range occupied by each component(e.g., RGB, YUV, YCrCb, etc.) of a signal captured in P3 or BT.709 colorgamut may be reduced in a BT.2020 representation. Since the data isrepresented in floating point accuracy, there is no loss; however, whencombined with color conversion (e.g., a conversion from RGB to YCrCBshown in equation 3 below) and quantization (example in equation 4below), the shrinking of the value range leads to increased quantizationerror for input data.

$\begin{matrix}{{{Y^{\prime} = {{0.2627*R^{\prime}} + {0.6780*G^{\prime}} + {0.0593*B^{\prime}}}};}{{{Cb} = \frac{B^{\prime} - Y^{\prime}}{1.8814}};}{{Cr} = \frac{R^{\prime} - Y^{\prime}}{1.4746}}} & (3)\end{matrix}$D _(Y′)=(Round((1<<(BitDepth_(Y)−8))*(219*Y′+16)))

D _(Cb)=(Round((1<<(BitDepth_(Cr)−8))*(224*Cb+128)))

D _(Cr)=(Round((1<(BitDepth_(Cb)−8))*(224*Cr+128)))   (4)

In equation (4) D_(Y′) is the quantized Y′ component, D_(Cb) is thequantized Cb and D_(Cr) is the quantized Cr component. The term<<represents a bit-wise right shift. BitDepth_(Y), BitDepth_(Cr), andBitDepth_(Cb) are the desired bit depths of the quantized components,respectively.

In addition, in a real-world coding system, coding a signal with reduceddynamic range may lead to significant loss of accuracy for coded chromacomponents and would be observed by a viewer as coding artifacts, e.g.,color mismatch and/or color bleeding.

To address the problems described above, the following techniques may beconsidered. One example technique involves HDR coding at the nativecolor space. In such a technique an HDR video coding system wouldsupport various types of currently known color gamuts, and allowextensions of a video coding standard to support future color gamuts.This support would not be only limited to support different colorconversion transforms, e.g. RGB to YCbCr, and their inverse transforms,but also would specify transform functions that are adjusted to each ofthe color gamuts. Support of such variety of tools would complex andexpensive.

Another example technique includes a color gamut aware video codec. Insuch a technique, a hypothetical video encoder is configured to estimatethe native color gamut of the input signal and adjust coding parameters(e.g., quantization parameters for coded chroma components) to reduceany distortion resulting from the reduced dynamic range. However, such atechnique would not be able to recover loss of accuracy, which mayhappen due to the quantization conducted in equation (4) above, sinceall input data is provided to a typical codec in integer point accuracy.

This disclosure describes techniques, methods, and apparatuses toperform a dynamic range adjustment (DRA) to compensate dynamic rangechanges introduced to HDR signal representations by a color gamutconversion. The dynamic range adjustment may help to prevent and/orlessen any distortion caused by a color gamut conversion, includingcolor mismatch, color bleeding, etc. In one or more examples of thedisclosure, DRA is conducted on the values of each color component ofthe target color space, e.g., YCbCr, prior to quantization at theencoder side (e.g., by source device 12) and after the inversequantization at the decoder side (e.g., by destination device 14).

FIG. 8 is a block diagram illustrating an example HDR/WCG conversionapparatus operating according to the techniques of this disclosure. InFIG. 8, solid lines specify the data flow and dashed lines specifycontrol signals. The techniques of this disclosure may be performed byvideo pre-processor unit 19 of source device 12. As discussed above,video pre-processor unit 19 may be a separate device from video encoder20. In other examples, video pre-processor unit 19 may be incorporatedinto the same device as video encoder 20.

As shown in FIG. 8, RGB native CG video data 200 is input to videopre-processor unit 19. In the context of video preprocessing by videopre-processor unit 19, RGB native CG video data 200 is defined by aninput color container. The input color container specifies set of colorprimaries used to represent video data 200 (e.g., BT. 709, BT. 2020, P3,etc.). In one example of the disclosure, video pre-processor unit 19 maybe configured to convert both the color container and the color space ofRGB native CB video data 200 to a target color container and targetcolor space for HDR′ data 216. Like the input color container, thetarget color container may specify a set or color primaries used torepresent the HDR′ data 216. In one example of the disclosure, RGBnative CB video data 200 may be HDR/WCG video, and may have a BT.2020 orP3 color container (or any WCG), and be in an RGB color space. Inanother example, RGB native CB video data 200 may be SDR video, and mayhave a BT.709 color container. In one example, the target colorcontainer for HDR′ data 216 may have been configured for HDR/WCG video(e.g., BT.2020 color container) and may use a color space more optimalfor video encoding (e.g., YCrCb).

In one example of the disclosure, CG converter 202 may be configured toconvert the color container of RGB native CG video data 200 from theinput color container (e.g., first color container) to the target colorcontainer (e.g., second color container). As one example, CG converter202 may convert RGB native CG video data 200 from a BT.709 colorrepresentation to a BT.2020 color representation, example of which isshown below.

The process to convert RGB BT.709 samples (R₇₀₉, G₇₀₉, B₇₀₉) to RGBBT.2020 samples (R₂₀₂₀, G₂₀₂₀, B₂₀₂₀) can be implemented with a two-stepconversion that involves converting first to the XYZ representation,followed by a conversion from XYZ to RGB BT.2020 using the appropriateconversion matrices.

X=0.412391*R ₇₀₉+0.357584*G ₇₀₉+0.180481*B ₇₀₉

Y=0.212639*R ₇₀₉+0.715169*G ₇₀₉+0.072192*B ₇₀₉

Z=0.019331*R ₇₀₉+0.119195*G ₇₀₉+0.950532*B ₇₀₉  (5)

Conversion from XYZ to R₂₀₂₀G₂₀₂₀B₂₀₂₀ (BT.2020)

R ₂₀₂₀=clipRGB(1.716651*X−0.355671*Y−0.253366*Z)

G ₂₀₂₀=clipRGB(−0.666684*X+1.616481*Y+0.015768*Z)

B ₂₀₂₀=clipRGB(0.017640*X−0.042771*Y+0.942103*Z)  (6)

Similarly, the single step and recommended method is as follows:

R ₂₀₂₀=clipRGB(0.627404078626*R ₇₀₉+0.329282097415*G₇₀₉+0.043313797587*B ₇₀₉)

G2020=clipRGB(0.069097233123*R ₇₀₉+0.919541035593*G ₇₀₉+0.011361189924*B₇₀₉)

B ₂₀₂₀=clipRGB(0.016391587664*R ₇₀₉+0.088013255546*G₇₀₉+0.895595009604*B ₇₀₉)  (7)

The resulting video data after CG conversion is shown as RGB target CGvideo data 204 in FIG. 8. In other examples of the disclosure, the colorcontainer for the input data and the output HDR′ data may be the same.In such an example, CG converter 202 need not perform any conversion onRGB native CG video data 200.

Next, transfer function unit 206 compacts the dynamic range of RGBtarget CG video data 204. Transfer function unit 206 may be configuredto apply a transfer function to compact the dynamic range in the samemanner as discussed above with reference to FIG. 5. The color conversionunit 208 converts RGB target CG color data 204 from the color space ofthe input color container (e.g., RGB) to the color space of the targetcolor container (e.g., YCrCb). As explained above with reference to FIG.5, color conversion unit 208 converts the compacted data into a morecompact or robust color space (e.g., a YUV or YCrCb color space) that ismore suitable for compression by a hybrid video encoder (e.g., videoencoder 20).

Adjustment unit 210 is configured to perform a dynamic range adjustment(DRA) of the color converted video data in accordance with DRAparameters derived by DRA parameters estimation unit 212. In general,after CG conversion by CG converter 202 and dynamic range compaction bytransfer function unit 206, the actual color values of the resultingvideo data may not use all available codewords (e.g., unique bitsequences that represent each color) allocated for the color gamut of aparticular target color container. That is, in some circumstances, theconversion of RGB native CG video data 200 from an input color containerto an output color container may overly compact the color values (e.g.,Cr and Cb) of the video data such that the resultant compacted videodata does not make efficient use of all possible color representations.As explained above, coding a signal with a reduced range of values forthe colors may lead to a significant loss of accuracy for coded chromacomponents and would be observed by a viewer as coding artifacts, e.g.,color mismatch and/or color bleeding.

Adjustment unit 210 may be configured to apply DRA parameters to thecolor components (e.g., YCrCb) of the video data, e.g., RGB target CGvideo data 204 after dynamic range compaction and color conversion tomake full use of the codewords available for a particular target colorcontainer. Adjustment unit 210 may apply the DRA parameter to the videodata at a pixel level. In general, the DRA parameters define a functionthat expands the codewords used to represent the actual video data to asmany of the codewords available for the target color container aspossible.

In one example of the disclosure, the DRA parameters include a scale andoffset value that is applied to the components of the video data. Ingeneral, the lower the value range of the color components of the videodata, the larger a scaling factor may be used. The offset parameter maybe used to center the values of the color components to the center ofthe available codewords for a target color container. For example, if atarget color container includes 1024 codewords per color component, anoffset value may be chosen such that the center codeword is moved tocodeword 512 (e.g., the middle most codeword). In other examples, theoffset parameter may be used to provide better mapping of inputcodewords to output codewords such that overall representation in thetarget color container is more efficient in combating coding artefacts.

In one example, adjustment unit 210 applies DRA parameters to video datain the target color space (e.g., YCrCb) as follows:

Y″=scale1*Y′+offset1

Cb″=scale2*Cb′+offset2

Cr″=scale3*Cr′+offset3  (8)

where signal components Y′, Cb′ and Cr′ is a signal produced from RGB toYCbCr conversion (example in equation 3). Note that Y′, Cr′ and Cr′ mayalso be a video signal decoded by video decoder 30. Y″, Cb″, and Cr″ arethe color components of the video signal after the DRA parameters havebeen applied to each color component. As can be seen in the exampleabove, each color component is related to different scale and offsetparameters. For example, scale1 and offset1 are used for the Y′component, scale2 and offset2 are used for the Cb′ component, and scale3and offset3 are used for the Cr′ component. It should be understood thatthis is just an example. In other examples, the same scale and offsetvalues may be used for every color component.

In other examples, each color component may be associated with multiplescale and offset parameters. For example, the actual distribution ofchroma values for the Cr or Cb color components may differ for differentpartitions or ranges of codewords. As one example, there may be moreunique codewords used above the center codeword (e.g., codeword 512)than there are below the center codeword. In such an example, adjustmentunit 210 may be configured to apply one set of scale and offsetparameters for chroma values above the center codeword (e.g., havingvalues greater than the center codeword) and apply a different set ofscale and offset parameters for chroma values below the center codeword(e.g., having values less than the center codeword).

As can be seen in the above example, adjustment unit 210 applies thescale and offset DRA parameters as a linear function. As such, it is notnecessary for adjustment unit 210 to apply the DRA parameters in thetarget color space after color conversion by color conversion unit 208.This is because color conversion is itself a linear process.

As such, in other examples, adjustment unit 210 may apply the DRAparameters to the video data in the native color space (e.g., RGB)before any color conversion process. In this example, color conversionunit 208 would apply color conversion after adjustment unit 210 appliesthe DRA parameters.

In another example of the disclosure, adjustment unit 210 may apply theDRA parameters in either the target color space or the native colorspace as follows:

Y″=(scale1*(Y′−offsetY)+offset1)+offsetY;

Cb″=scale2*Cb′+offset2

Cr″=scale3*Cr′+offset3

In this example, the parameter scale1, scale2, scale3, offset1, offset2,and offset3 have the same meaning as described above. The parameteroffsetY is a parameter reflecting brightness of the signal, and can beequal to the mean value of Y′. In other examples, an offset parametersimilar to offsetY may be applied for the Cb‘ and Cr’ components tobetter preserve the mapping of the center value in the input and theoutput representations.

In another example of the disclosure, adjustment unit 210 may beconfigured to apply the DRA parameters in a color space other than thenative color space or the target color space. In general, adjustmentunit 210 may be configured to apply the DRA parameters as follows:

A′=scale1*A+offset1;

B′=scale2*B+offset2

C′=scale3*C+offset3  (10)

where signal components A, B and C are signal components in a colorspace which is different from target color space, e.g., RGB or anintermediate color space.

In other examples of the disclosure, adjustment unit 210 is configuredto apply a linear transfer function to the video to perform DRA. Such atransfer function is different from the transfer function used bytransfer function unit 206 to compact the dynamic range. Similar to thescale and offset terms defined above, the transfer function applied byadjustment unit 210 may be used to expand and center the color values tothe available codewords in a target color container. An example ofapplying a transfer function to perform DRA is shown below:

Y″=TF2(Y′)

Cb″=TF2(Cb′)

Cr″=TF2(Cr′)

Term TF2 specifies the transfer function applied by adjustment unit 210.In some examples, adjustment unit 210 may be configured to applydifferent transfer functions to each of the components.

In another example of the disclosure, adjustment unit 210 may beconfigured to apply the DRA parameters jointly with the color conversionof color conversion unit 208 in a single process. That is, the linearfunctions of adjustment unit 210 and color conversion unit 208 may becombined. An example of a combined application, where f1 and f2 are acombination of the RGB to YCbCr matrix and the DRA scaling factors, isshown below:

${{Cb} = \frac{B^{\prime} - Y^{\prime}}{f\; 1}};$${Cr} = \frac{R^{\prime} - Y^{\prime}}{f\; 2}$

In another example of the disclosure, after applying the DRA parameters,adjustment unit 210 may be configured to perform a clipping process toprevent the video data from having values outside the range of codewordsspecified for a certain target color container. In some circumstances,the scale and offset parameters applied by adjustment unit 210 may causesome color component values to exceed the range of allowable codewords.In this case, adjustment unit 210 may be configured to clip the valuesof the components that exceed the range to the maximum value in therange.

The DRA parameters applied by adjustment unit 210 may be determined byDRA parameters estimation unit 212. The frequency and the time instancesat which the DRA parameters estimation unit 212 updates the DRAparameters are flexible. For example, DRA parameters estimation unit 212may update the DRA parameters on a temporal level. That is, new DRAparameters may be determined for a group of pictures (GOP), or a singlepicture (frame). In this example, the RGB native CG video data 200 maybe a GOP or a single picture. In other examples, DRA parametersestimation unit 212 may update the DRA parameters on a spatial level,e.g., at the slice tile, or block level. In this context, a block ofvideo data may be a macroblock, coding tree unit (CTU), coding unit, orany other size and shape of block. A block may be square, rectangular,or any other shape. Accordingly, the DRA parameters may be used for moreefficient temporal and spatial prediction and coding.

In one example of the disclosure, DRA parameters estimation unit 212 mayderive the DRA parameters based on the correspondence of the nativecolor gamut of RGB native CG video data 200 and the color gamut of thetarget color container. For example, DRA parameters estimation unit 212may use a set of predefined rules to determine scale and offset valuesgiven a certain native color gamut (e.g., BT.709) and the color gamut ofa target color container (e.g., BT.2020).

For example, assume that native color gamut and target color containerare defined in the form of color primaries coordinates in xy space andwhite point coordinates. One example of such information for BT.709 andBT.2020 is shown in Table 2 below.

TABLE 2 RGB color space parameters RGB color space parameters ColorWhite point Primary colors space xx_(W) yy_(W) xx_(R) yy_(R) xx_(G)yy_(G) xx_(B) yy_(B) DCI-P3 0.314 0.351 0.680 0.320 0.265 0.690 0.1500.060 ITU-R 0.3127 0.3290 0.64 0.33 0.30 0.60 0.15 0.06 BT.709 ITU-R0.3127 0.3290 0.708 0.292 0.170 0.797 0.131 0.046 BT.2020

In one example, BT.2020 is the color gamut of the target color containerand BT.709 is the color gamut of the native color container. In thisexample, adjustment unit 210 applies the DRA parameters to the YCbCrtarget color space. DRA parameters estimation unit 212 may be configuredto estimate and forward the DRA parameters to adjustment unit 210 asfollows:

scale1=1; offset1=0;

scale2=1.0698; offset2=0;

scale3=2.1735; offset3=0;

As another example, with BT.2020 being a target color gamut and P3 beinga native color gamut, and DRA being applied in YCbCr target color space,DRA parameters estimation unit 212 may be configured to estimate the DRAparameters as:

scale1=1; offset1=0;

scale2=1.0068; offset2=0;

scale3=1.7913; offset3=0;

In the examples above, DRA parameters estimation unit 212 may beconfigured to determine the above-listed scale and offset values byconsulting a lookup table that indicates the DRA parameters to use,given a certain native color gamut and a certain target color gamut. Inother examples, DRA parameters estimation unit 212 may be configured tocalculate the DRA parameters from the primary and white space values ofthe native color gamut and target color gamut, e.g., as shown in Table2.

For example, consider a target (T) color container specified by primarycoordinates (xXt, yXt), where X stated for R,G,B color components:

${primeT} = \begin{bmatrix}{xRt} & {yRt} \\{xGt} & {yGt} \\{xBt} & {yBt}\end{bmatrix}$

and native (N) color gamut specified by primaries coordinates (xXn,yXn), where X stated for R,G,B color components:

${primeN} = \begin{bmatrix}{xRn} & {yRn} \\{xGn} & {yGn} \\{xBn} & {yBn}\end{bmatrix}$

The white point coordinate for both gamuts equals whiteP=(xW,yW). DRAparameters estimation unit 212 may derive the scale2 and scale3parameters for DRA as a function of the distances between primariescoordinates to the white point. One example of such an estimation isgiven below:

rdT=sqrt((primeT(1,1)−whiteP(1,1))̂2+(primeN(1,2)−whiteP(1,2))̂2)

gdT=sqrt((primeT(2,1)−whiteP(1,1))̂2+(primeN(2,2)−whiteP(1,2))̂2)

bdT=sqrt((primeT(3,1)−whiteP(1,1))̂2+(primeN(3,2)−whiteP(1,2))̂2)

rdN=sqrt((primeN(1,1)−whiteP(1,1))̂2+(primeN(1,2)−whiteP(1,2))̂2)

gdN=sqrt((primeN(2,1)−whiteP(1,1))̂2+(primeN(2,2)−whiteP(1,2))̂2)

bdN=sqrt((primeN(3,1)−whiteP(1,1))̂2+(primeN(3,2)−whiteP(1,2))̂2)

scale2=bdT/bdN

scale3=sqrt ((rdT/rdN)̂2+(gdT/gdN)̂2)

In some examples, DRA parameters estimation unit 212 may be configuredto estimate the DRA parameters by determining the primaries coordinatesin primeN from the actual distribution of color values in RGB native CGvideo data 200, and not from the pre-defined primary values of thenative color gamut. That is, DRA parameters estimation unit 212 may beconfigured to analyze the actual colors present in RGB native CG videodata 200, and use the primary color values and white point determinedfrom such an analysis in the function described above to calculate DRAparameters. Approximation of some parameters defined above might be usedas DRA to facilitate the computation. For instance, scale3=2.1735 can beapproximated to scale3=2, which allows for easier implementation in somearchitectures.

In other examples of the disclosure, DRA parameters estimation unit 212may be configured to determine the DRA parameters based not only on thecolor gamut of the target color container, but also on the target colorspace. The actual distributions of values of component values may differfrom color space to color space. For example, the chroma valuedistributions may be different for YCbCr color spaces having a constantluminance as compared to YCbCr color spaces having a non-constantluminance. DRA parameters estimation unit 212 may use the colordistributions of different color spaces to determine the DRA parameters.

In other examples of the disclosure, DRA parameters estimation unit 212may be configured to derive values for DRA parameters so as to minimizecertain cost functions associated with pre-processing and/or encodingvideo data. As one example, DRA parameters estimation unit 212 may beconfigured to estimate DRA parameters that minimized quantization errorsintroduced by quantization unit 214 (e.g., see equation (4)) above. DRAparameters estimation unit 212 may minimize such an error by performingquantization error tests on video data that has had different sets ofDRA parameters applied. In another example, DRA parameters estimationunit 212 may be configured to estimate DRA parameters that minimize thequantization errors introduced by quantization unit 214 in a perceptualmanner. DRA parameters estimation unit 212 may minimize such an errorbased on perceptual error tests on video data that has had differentsets of DRA parameters applied. DRA parameters estimation unit 212 maythen select the DRA parameters that produced the lowest quantizationerror.

In another example, DRA parameters estimation unit 212 may select DRAparameters that minimize a cost function associated with both the DRAperformed by adjustment unit 210 and the video encoding performed byvideo encoder 20. For example, DRA parameters estimation unit 212 mayperform DRA and encode the video data with multiple different sets ofDRA parameters. DRA parameters estimation unit 212 may then calculate acost function for each set of DRA parameters by forming a weighted sumof the bitrate resulting from DRA and video encoding, as well as thedistortion introduced by these two lossy process. DRA parametersestimation unit 212 may then select the set of DRA parameters thatminimizes the cost function.

In each of the above techniques for DRA parameter estimation, DRAparameters estimation unit 212 may determine the DRA parametersseparately for each component using information regarding thatcomponent. In other examples, DRA parameters estimation unit 212 maydetermine the DRA parameters using cross-component information. Forexample, the DRA parameters derived for a Cr component may be used toderive DRA parameters for a Cb component.

In addition to deriving DRA parameters, DRA parameters estimation unit212 may be configured to signal the DRA parameters in an encodedbitstream. DRA parameters estimation unit 212 may signal one or moresyntax elements that indicate the DRA parameters directly, or may beconfigured to provide the one or more syntax elements to video encoder20 for signaling. Such syntax elements of the parameters may be signaledin the bitstream such that video decoder 30 and/or video post-processorunit 31 may perform the inverse of the process of video pre-processorunit 19 to reconstruct the video data in its native color container.Example techniques for signaling the DRA parameters are discussed below.

In one example, DRA parameters estimation unit 212 may signal one ormore syntax elements that in an encoded video bitstream as metadata, ina supplemental enhancement information (SEI) message, in video usabilityinformation (VUI), in a video parameter set (VPS), in a sequenceparameter set (SPS), in a picture parameter set, in a slice header, in aCTU header, or in any other syntax structure suitable for indicating theDRA parameters for the size of the video data (e.g., GOP, pictures,blocks, macroblock, CTUs, etc.).

In some examples, the one or more syntax elements indicate the DRAparameters explicitly. For example, the one or more syntax elements maybe the various scale and offset values for DRA. In other examples, theone or more syntax elements may be one or more indices into a lookuptable that includes the scale and offset values for DRA. In stillanother example, the one or more syntax elements may be indices into alookup table that specifies the linear transfer function to use for DRA.

In other examples, the DRA parameters are not signaled explicitly, butrather, both video pre-processor unit 19 and video post-processor unit31 are configured to derive the DRA parameters using the samepre-defined process using the same information and/or characteristics ofthe video data that are discernible form the bitstream. As one example,video post-processor unit 31 may be configured to indicate the nativecolor container of the video data as well as the target color containerof the encoded video data in the encoded bitstream. Video post-processorunit 31 may then be configured to derive the DRA parameters from suchinformation using the same process as defined above. In some examples,one or more syntax elements that identify the native and target colorcontainers are supplied in a syntax structure. Such syntax elements mayindicate the color containers explicitly, or may be indices to a lookuptable. In another example, video pre-processor unit 19 may be configuredto signal one or more syntax elements that indicate the XY values of thecolor primaries and the white point for a particular color container. Inanother example, video pre-processor unit 19 may be configured to signalone or more syntax elements that indicate the XY values of the colorprimaries and the white point of the actual color values (contentprimaries and content white point) in the video data based on ananalysis performed by DRA parameters estimation unit 212.

As one example, the color primaries of the smallest color gamutcontaining the color in the content might be signaled, and at videodecoder 30 and/or video post-processor unit 31, the DRA parameters arederived using both the container primaries and the content primaries. Inone example, the content primaries can be signaled using the x and ycomponents for R, G and B, as described above. In another example, thecontent primaries can be signaled as the ratio between two known primarysets. For example, the content primaries can be signaled as the linearposition between the BT.709 primaries and the BT.2020 primaries: x_(r)_(_) _(content)=alfa_(r)*x_(r) _(_) _(bt709)+(1−alfa_(r))*x_(r) _(_)_(bt2020) (with similar equation with alfa_(g) and alfa_(b) for the Gand B components), where parameter alfa_(r) specifies a ratio betweentwo known primary sets. In some examples, the signaled and/or derivedDRA parameters may be used by video encoder 20 and/or video decoder 30to facilitate weighted prediction based techniques utilized for codingof HDR/WCG video data.

In video coding schemes utilizing weighted prediction, a sample ofcurrently coded picture Sc are predicted from a sample (for singledirectional prediction) of the reference picture Sr taken with a weight(W_(wp)) and an offset (O_(wp)) which results in predicted sample Sp:

Sp=Sr·*W _(wp) +O _(wp).

In some examples utilizing DRA, samples of the reference and currentlycoded picture can be processed with DRA employing different parameters,namely {scale1_(cur), offset1_(cur)} for a current picture and{scale1_(ref), offset1_(ref)} for a reference picture. In suchembodiments, parameters of weighted prediction can be derived from DRA,e.g.:

W _(wp)=scale1_(cur)/scale1_(ref)

O _(wp)=offset1_(cur)−offset1_(ref)

After adjustment unit 210 applies the DRA parameters, videopre-processor unit 19 may then quantize the video data usingquantization unit 214. Quantization unit 214 may operate in the samemanner as described above with reference to FIG. 4. After quantization,the video data is now adjusted in the target color space and targetcolor gamut of the target primaries of HDR′ data 216. HDR′ data 216 maythen be sent to video encoder 20 for compression.

FIG. 9 is a block diagram illustrating an example HDR/WCG inverseconversion apparatus according to the techniques of this disclosure. Asshown in FIG. 9, video post-processor unit 31 may be configured to applythe inverse of the techniques performed by video pre-processor unit 19of FIG. 8. In other examples, the techniques of video post-processorunit 31 may be incorporated in, and performed by, video decoder 30.

In one example, video decoder 30 may be configured to decode the videodata encoded by video encoder 20. The decoded video data (HDR′ data 316in the target color container) is then forwarded to video post-processorunit 31. Inverse quantization unit 314 performs an inverse quantizationprocess on HDR′ data 316 to reverse the quantization process performedby quantization unit 214 of FIG. 8.

Video decoder 30 may also be configured to decode and send any of theone or more syntax elements produced by DRA parameters estimation unit212 of FIG. 8 to DRA parameters derivation unit 312 of videopost-processor unit 31. DRA parameters derivation unit 312 may beconfigured to determine the DRA parameters based on the one or moresyntax elements, as described above. In some examples, the one or moresyntax elements indicate the DRA parameters explicitly. In otherexamples, DRA parameters derivation unit 312 is configured to derive theDRA parameters using the same techniques used by DRA parametersestimation unit 212 of FIG. 8.

The parameters derived by DRA parameters derivation unit 312 are sent toinverse adjustment unit 310. Inverse adjustment unit 310 uses the DRAparameters to perform the inverse of the linear DRA adjustment performedby adjustment unit 210.

Inverse adjustment unit 310 may apply the inverse of any of theadjustment techniques described above for adjustment unit 210. Inaddition, as with adjustment unit 210, inverse adjustment unit 310 mayapply the inverse DRA before or after any inverse color conversion. Assuch, inverse adjustment unit 310 may apply the DRA parameter on thevideo data in the target color container or the native color container.In some examples, inverse adjustment unit 310 may be positioned to applyinverse adjustment before inverse quantization unit 314.

Inverse color conversion unit 308 converts the video data from thetarget color space (e.g., YCbCr) to the native color space (e.g., RGB).Inverse transfer function 306 then applies an inverse of the transferfunction applied by transfer function 206 to uncompact the dynamic rangeof the video data. In some examples, he resulting video data (RGB targetCG 304) is still in the target color gamut, but is now in the nativedynamic range and native color space. Next, inverse CG converter 302converts RGB target CG 304 to the native color gamut to reconstruct RGBnative CG 300.

In some examples, additional post-processing techniques may be employedby video post-processor unit 31. Applying the DRA may put the videooutside its actual native color gamut. The quantization steps performedby quantization unit 214 and inverse quantization unit 314, as well asthe up and down-sampling techniques performed by adjustment unit 210 andinverse adjustment unit 310, may contribute to the resultant colorvalues in the native color container being outside the native colorgamut. When the native color gamut is known (or the actual smallestcontent primaries, if signaled, as described above), then additionalprocess can be applied to RGB native CG video data 304 to transformcolor values (e.g., RGB or Cb and Cr) back into the intended gamut aspost-processing for DRA. In other examples, such post-processing may beapplied after the quantization or after DRA application.

As mentioned above, several SEI messages may be used to convey theinformation regarding dynamic range adjustment information for thevarious color components of the video data. The component scaling SEImessage, such as described above and in more detail below, may convey aset of scale factors, offsets, and ranges (e.g., partitions of codewordvalues) that can be used to indicate the mapping information for thevarious color components of the video data. The mapping information maybe used to indicate to video decoder 30 and/or video post-processor unit31 how to expand or shrink the different ranges of sample values in sucha way that the overall quality of the reconstructed HDR video data, oralso quality of reconstructed SDR video data in some cases wherebackward compatibility is desired, is improved, or to make thereconstructed output more suitable for display capabilities.

Table 3 below provides one variation of the syntax structure of acomponent scaling SEI message. Note that although the names of thesyntax elements below contain the prefix “hdr_recon_” that is differentfrom that described in the examples below, where the names of the syntaxelements are prefixed as component_scaling, the syntax table isotherwise the same.

TABLE 3 Example Range Adjustment SEI syntax De- scrip- torhdr_reconstruction_info( payloadSize ) { hdr_recon_id ue(v)hdr_recon_cancel_flag u(1) if( !hdr_recon_cancel_flag ) {hdr_recon_persistence_flag u(1) hdr_recon_transfer_characteristics u(8)hdr_recon_default_flag u(1) if( !hdr_recon_default_flag ) {hdr_recon_scale_bit_depth u(4) hdr_recon_offset_bit_depth u(4)hdr_recon_scale_frac_bit_depth u(4) hdr_recon_offset_frac_bit_depth u(4)hdr_recon_num_comps_minus1 ue(v) } for( c = 0; c <=hdr_recon_num_comps_minus1; c++ ) { hdr_recon_num_ranges[ c ] ue(v)hdr_recon_equal_ranges_flag[ c ] u(1) hdr_recon_global_offset_val[ c ]u(v) for( i = 0; i <= hdr_recon_num_ranges[ c ]; i++ )hdr_recon_scale_val[ c ][ i ] u(v) if( !hdr_recon_equal_ranges[ c ] )for( i = 0; i <= hdr_recon_num_ranges[ c ]; i++ ) hdr_recon_range_val [c ][ i ] u(v) } } }

The semantics of the SEI syntax of Table 3 is presented below.

The mapping process is based on piece-wise linear functions map[c]( ),for c=0 . . . hdr_recon_num_comps_minus1, that map a value x in[0,1] toa value y=map[c](x) as follows:

-   For i in the range of 0 to hdr_recon_num_ranges[ c ] − 1, inclusive,the following applies: -   The value ScaleValue[ c ][ i ] is derived asdescribed in semantics of syntax element hdr_recon_scale_val[ c ][ i]. -   The value RangeValue[ c ][ i ] is derived as described insemantics of syntax element hdr_recon_range_val[ c ][ i ].

-   -   The values InputRanges[c][i] and OutputRanges[c][i], for i in        the range of 0 to hdr_recon_num_ranges[c]−1, inclusive, are        derived as follows:

-   If i is equal to 0, the following applies: OutputRanges[ c ][ i ] =− hdr_recon_global_offset_val[ c ] * ScaleValue[ c ][ i − 1 ] (D- xx)InputRanges[ c ][ i ] = 0 (D-xx) -   Otherwise (i is not equal to 0),the following applies: InputRanges[ c ][ i ] = InputRanges[ c ][ i − 1] + RangeValue[ c ][ i − 1 ] (D-xx) OutputRanges[ c ][ i ] =OutputRanges[ c ][ i − 1 ] + RangeValue[ c ][ i − 1 ] * ScaleValue[ c ][i − 1 ] (D-xx)

-   -   The values OffsetValue[c][i], for i in the range of 0 to        hdr_recon_num_ranges[c]−1, inclusive, are derived as follows:

OffsetValue[ c ][ i ] = InputRanges[ c ][ i + 1 ] − OutputRanges[ c ] [i + 1 ] □ ScaleValue[ c ][ i − 1 ]   (D-xx)

-   -   The parameter y=map[c](x) is derived as follows:

-   If x is lower than or equal to OutputRanges[ c ][ 0 ], the followingapplies: y = InputRanges[ c ][ 0 ]         (D-xx) -   Otherwise if x islarger than OutputRanges[ c ][ hdr_recon_num_ranges[ c ] ], thefollowing applies: y = InputRanges[ c ][ hdr_recon_num_ranges[ c ] ](D-xx) -   Otherwise, the following applies:      for( i = 1; i <=hdr_recon_num_ranges[ c ]; i++ )        if( OutputRanges[ i − 1 ] < x &&x < = OutputRanges[ i ] )          y = x ÷ ScaleValue[ c ][ i − 1 ] +OffsetValue[ c ][ i − 1 ] (D-xx)

Several problems have been identified that are associated with thecomponent scaling information SEI messages, and other parameters thatare applicable to adjust the dynamic range of components. In particular,problems have been identified related to the use of floating pointnumbers to derive scale and offset values, as well as the ranges ofcodewords for sample values (e.g., RGB values, YCrCb values, YUV values,XYZ values, etc.). For example, the scale values that are signalled inthe bitstream are used at the decoder side, for example, by videopost-processor 31, to perform an inverse dynamic range adjustmentprocess. However, in order to use the scale values for computing theranges of sample values, and for computing the mapping process, areciprocal operation is performed at video post-processor 31. Previousexample semantics for a component scaling SEI message specify the use ofthe reciprocal (e.g., the reciprocal of a scale value, or reciprocal ofa scale value and an added offset value) to be multiplied with samplevalues. Errors introduced in such a reciprocal operation would be moresignificant than potential errors in a forward operation, as thereciprocal is applied to every sample value generated.

The semantics of the component scaling SEI message indicates thederivation process of the ranges of sample values, and the mappingprocess (e.g., the application of scale and offset values) to each rangeof codewords of color components (e.g., sample values) in terms offloating point operations. This could lead to differences in thereconstructed HDR output based on the various floating point arithmeticimplementations in different computing systems.

This application describes several techniques to improve thecommunication of component scaling information using SEI signaling andprocessing, or other similar signaling techniques which may be specifiedin video coding standards, such as H.265/HEVC, H.264/AVC, BDA, MPEG orothers. It is to be recognized that one or more of the following aspectsmay be applied independently, or in suitable combination with others ofthese aspects in any particular example.

In general, this disclosure describes techniques wherein video encoder20 and/or video pre-processor unit 19 may be configured to signal ascale value for one or more sample value ranges of a component samplevalues (e.g., color component values). The scale value is specified suchthat video decoder 30 and video post-processor unit 31 may be configuredto perform a mapping process to obtain an output sample value from theinput sample value of the component by multiplying the scale valuespecified for a specific sample value range containing the input samplevalue with the input sample value and adding an offset computed based onthe parameters as part of the component scaling information.

In another example of the disclosure, rather than using a floating pointimplementation to compute the size and number of ranges of codewords ofa color component, video encoder 20 and/or video pre-processor unit 19may be configured to derive the size and number of ranges of codewordsof the color component using a fixed-point computing implementation. Forexample, video encoder 20 and/or video pre-processor unit 19 may beconfigured to use a predetermined number of fractional bits fordetermining and applying the parameters of the dynamic range adjustmentmapping process. Note that the number of fractional bits may bedifferent for each parameter (e.g., range of values for each colorcomponent (codeword), scale value, and offset value) of the dynamicrange adjustment process.

For example, video pre-processor unit 19 may be configured to performinteger operations on any parameters or syntax element (e.g.hdr_recon_num_ranges[c]) used to communicate the size and number ofranges of codewords for a color component. Video pre-processor unit 19may be configured to keep track of the number of bits used by thefractional part of any calculation of the size and number of ranges inthe fixed-point implementation used. Video pre-processor unit 19 and/orvideo encoder 20 may be configured to signal the number of bits used inthe fractional part in an SEI message (e.g.,hdr_recon_offset_frac_bit_depth, hdr_recon_scale_frac_bit_depth), or thenumber of bits used in the fractional part may be a pre-determinedvalue. Video decoder 30 may be configured to decode the syntax elementsin the SEI message indicating the number of bits in the fractional partand video post-processor unit 31 may be configured to perform an inversedynamic range adjustment using the same number of bits in the fractionalpart for one or more of the parameters of the inverse dynamic rangeadjustment process.

In one example of the disclosure, when determining the ranges and/orother parameters for the mapping process, video decoder 30 and/or videopost-processor unit 31 may be configured to determine such parameters sothat, when the signaled fractional bit depths of different parametersare different, the accuracy of the computations performed for theparameters are retained as far as possible. For example, video decoder30 and/or video post-processor unit 31 may be configured to retain anyerrors introduced due to rounding to a minimum by accumulating thenumber of fractional bits in any intermediate calculation steps used todetermine a particular parameter. Video decoder 30 and/or videopost-processor unit 31 may then perform a clipping process to bring thefinal value of a particular parameter to the desired fractional accuracyat the last step of determining and/or calculating a particularparameter. In another example, when the signaled fractional bit depthsof the parameters are the same, video decoder 30 and/or videopost-processor unit 31 may be configured to accumulate the number offractional bits in the intermediate steps, and perform clipping to bringthe final value of a parameter to the desired accuracy at the laststep(s).

In another example, video decoder 30 and/or video post-processor unit 31may be configured to clip and/or truncate the value of a parameter atone or more intermediate steps of a calculation process or the parametersuch that the fractional parts of values obtained for the parameter arereduced to a pre-determined value. That is, rather than waiting untildetermining a final value for the parameter to perform any clipping,video decoder 30 and/or video post-processor unit 31 may clipintermediate values of calculations performed to determine theparameter. Such clipping or truncation may be based on the number offractional bits indicated in the SEI message. In another example, videodecoder 30 and/or video post-processor unit 31 may be configured to clipand/or truncate intermediate values used when calculating a particularparameter before a particular operation/step when it is determined that,if the operation/step is performed without clipping, the accumulatednumber of fractional bits would exceed a certain pre-determined value,e.g. the bit depth of the registers used to store the intermediatevalues.

In another example of the disclosure, video pre-processor unit 19 and/orvideo post-processor unit 31 may be configured to derive scale, offsetand range values according to predetermined sample value ranges based ona defined minimum and maximum values defined for the fixedrepresentation of the color components. For example, a fixedrepresentation of color components may have a plurality of ranges ofvalues defined, e.g., a “standard” range of values, a “full” range ofvalues, and a “restricted” range values. The “full” range of values mayhave a larger span between the minimum and maximum value of a particularcomponent (e.g., for an 8-bit full-range representation of YCbCr colorspace, the Y, Cb, and Cr components can take values in the rage of 0 to255, inclusive) as compared to the “standard” range of values (e.g., an8-bit standard range representation of YCbCr color space, the Ycomponent may take values in the range of 16 to 235, inclusive, and theCb and Cr components may take values between 16 and 240, inclusive). The“restricted” range of values may have a smaller span between the minimumand maximum value of a particular component (e.g., for a 10-bitrestricted-range representation of YCbCr color space, the Y, Cb, and Crcomponents may take values in the range of 4 to 1019, inclusive) ascompared to the “standard” range of values.

In one example, video encoder 20 and/or video pre-processor unit 19 maybe configured to signal a syntax element (e.g., in an SEI message) toindicate to video decoder 30 and/or video post-processor unit 31 theminimum and maximum permitted values of the samples (e.g., colorcomponent values) based on what sample range is used (e.g. full,restricted, standard, or others). In another example, video encoder 20and/or video pre-processor unit 19 may be configured to signal one ormore syntax values (e.g., in an SEI message) that indicate the minimumand maximum permitted values of the samples to video decoder based onwhat sample range is used (e.g. full, restricted, standard). Videodecoder 30 and/or video post-processor unit 31 may then determine therange of component values allowed for the inverse dynamic rangeadjustment process based on the received minimum value and the receivedmaximum value.

In another example, video encoder 20 and/or video pre-processor unit 19may be configured to signal a flag (e.g., in an SEI message) to indicatewhether the scale values are signed or unsigned. In this example, theparsing process of any SEI messages is the same regardless the value ofthe flag.

The following section includes several examples of embodiments that useexample techniques disclosed in the previous section. In thisembodiment, the component scaling function is signaled as a lookup tableand the number of bits used to signal the points defining the lookuptable are also signaled. In one example, the lookup defines a piece-wiselinear mapping function. The points for the lookup table correspond tothe (x,y) coordinates that define the piece-wise linear mapping. Forsample values that do not have explicit points signaled, the value isinterpolated based on the neighboring pivot points.

The derivation process of the ranges and the output sample values aredefined as below.

The mapping of sample x from component c to sample y=map[c](x) isspecified as follows:

-   -   Set the value of DefaultPrecShift equal to 9    -   Let the variables minSampleVal and maxSampleVal denote the        minimum and the maximum sample values as defined by the sample        range of the content.    -   The variable ScaleValue[c][i], for i in the range of 0 to        hdr_recon_num_ranges[c]−1, inclusive, is derived as follows:

SignValue[ c ][ i ] = 0 // 0 for positive, 1 for negativehdrReconScaleBitDepth = hdr_recon_scale_bit_depth − (hdr_negative_scales_present_flag ? 1 : 0 ) if(hdr_negative_scales_present_flag ) ScaleValue[ c ][ i ] =hdr_recon_scale_val[ c ][ i ] & ( (1 << hdrReconScaleBitDepth ) − 1 )(D-xx) SignValue[ c ][ i ] = hdr_recon_scale_val[ c ][ i ] & ( 1 <<hdrReconScaleBitDepth ) else ScaleValue[ c ][ i ] = hdr_recon_scale_val[c ][ i ] (D-xx) shiftInvScale = 1 << hdrReconScaleBitDepthInvScaleValue[ c ][ i ] = ( 1 << (DefaultPrecShift +hdrReconScaleBitDepth) + shiftInvScale ) / ScaleValue[ c ][ i ]

-   -   The variable RangeValue[c][i], for i in the range of 0 to        hdr_recon_num_ranges[c]−1, inclusive, is derived as follows:

- If hdr_recon_equal_ranges_flag[ c ] is equal to 0, the followingapplies: RangeValue[ c ][ i ] = hdr_recon_range_val[ c ][ i ] (D-xx) -Otherwise ( hdr_recon_equal_ranges_flag[ c ] is equal to 1 ), thefollowing applies: RangeValue[ c ][ i ] = ( ( InputDynamicRangeValue <<hdr_recon_offset_frac_bit_depth) + ( ( hdr_recon_num_ranges[ c ] + 1 )<< 1 ) ) / hdr_recon_num_ranges[ c ] (D-xx)

-   -   where InputDynamicRangeValue is equal to 1 when the sample range        is normalized from 0 to 1.    -   The variables InputRanges[c][i] and OutputRanges[c][i], for i in        the range of 0 to hdr_recon_num_ranges[c], inclusive, are        derived as follows:

- If i is equal to 0, the following applies: OutputRanges[ c ][ i ] = −hdr_recon_global_offset_val[ c ] * InvScaleValue[ c ][ i − 1 ] (D-xx)InputRanges[ c ][ i ] = 0 (D-xx) - Otherwise (i is not equal to 0), thefollowing applies: InputRanges[ c ][ i ] = InputRanges[ c ][ i − 1 ] +RangeValue[ c ][ i − 1 ] (D- xx) OutputRanges[ c ][ i ] = OutputRanges[c ][ i − 1 ] + RangeValue[ c ][ i − 1 ] * InvScaleValue[ c ][ i − 1 ](D-xx)

-   -   The parameters OffsetValue[c][i], for i in the range of 0 to        hdr_recon_num_ranges[c]−1, inclusive, are derived as follows:

precOffsetDeltaBits = DefaultPrecShift + hdr_recon_scale_frac_bit_depthOffsetValue[ c ][ i ] = InputRanges[ c ][ i + 1 ] * (1 <<precOffsetDeltaBits) − OutputRanges[ c ][ i + 1 ] * ScaleValue[ c ][ i −1 ] (D- xx) OffsetValue[ c ][ i ] = ( ( OffsetValue[ c ][ i ] + ( 1 <<(BitDepth − 1) ) ) >> BitDepth ) * ( maxSampleVal − minSampleVal )

-   -   The parameter y=map[c](x) is derived as follows:

- Variable bitDepthDelta is set equal to DefaultPrecShift +hdr_recon_offset_frac_bit_depth − BitDepth - If ( x << bitDepthDelta )is lower than or equal to OutputRanges[ c ][ 0 ], the following applies:y = InputRanges[ c ][ 0 ] (D-xx) fracBitDepth =hdr_recon_offset_frac_bit_depth - Otherwise if ( x << bitDepthDelta ) islarger than OutputRanges[ c ][ hdr_recon_num_ranges[ c ] ], thefollowing applies: y = InputRanges[ c ][ hdr_recon_num_ranges[ c ]](D-xx) fracBitDepth = hdr_recon_offset_frac_bit_depth - Otherwise, thefollowing applies: fracBitDepth = DefaultPrecShift +hdr_recon_scale_frac_bit_depth + hdr_recon_offset_frac_bit_depth −BitDepth for( i = 1; i < = hdr_recon_num_ranges[ c ]; i++ ) if(OutputRanges[ i − 1 ] < ( x << bitDepthDelta ) && ( x << bitDepthDelta )< = OutputRanges[ i ] ) { rangeBitShift = DefaultPrecShift +hdr_recon_offset_frac_bit_depth − BitDepth y = ( x − minSampleVal ) *ScaleValue[ c ][ i − 1 ] * ( 1 << rangeBitDepth ) +  OffsetValue[ c ][ i− 1 ] + minSampleVal * ( 1 << fracBitDepth ) (D-xx) } - fracShiftOffset= 1 << (fracBitDepth − 1) y = ( y + fracShiftOffset ) >> fracBitDepth

Alternatively, the adjustment of the sample range based on minSampleValand maxSampleVal are not performed on the OffsetValue, but rather on theInputRanges and OutputRanges as follows:

deltaSampleVal = maxSampleval − minSampleVal deltaBitShift =DefaultPrecShift + hdr_recon_offset_frac_bit_depth sampleShift = ( 1 <<( BitDepth − 1) ) + ( minSampleVal << deltaBitShift ) ) OutputRanges[ c][ i ] = ( ( OutputRanges[ c ][ i ] * deltaSampleVal) + sampleShift) >>BitDepth deltaBitShift = DefaultPrecShift +hdr_recon_offset_frac_bit_depth sampleShift = ( 1 << ( BitDepth − 1) ) +( minSampleVal << deltaBitShift ) ) InputRanges[ c ][ i ] = ((InputRanges[ c ][ i ] * deltaSampleVal) + sampleShift) >> BitDepth

This disclosure provides several techniques to improve carriage ofcomponent scaling information using SEI signaling and processing orother means which is specified or to be specified in video codingstandards, such as H.265/HEVC, H.264/AVC, BDA, MPEG or others. One ormore of these techniques may be applied independently, or in combinationwith others. In addition, the techniques described above for signalingand/or using information in SEI messages for performing a fixed-pointimplementation of a dynamic range process may utilize one or more of thesyntax structures described below for signaling/receiving theinformation.

In some examples, video encoder 20 may signal one or more SEI messagesthat include global offset values, including, for each component, afirst offset value that determines a first unadjusted component valuebelow which all component values are clipped to the first componentvalue before applying dynamic range adjustment as described in thisdisclosure. Decoder 30 may receive one or more of such SEI messages,parse and/or decode the information in the SEI messages, and pass theinformation to the video post-processor 31.

In some examples, for each component, video encoder 20 may signal one ormore SEI messages that include a second offset value that specifies theadjusted value to which the first offset value maps to after dynamicrange adjustment. Video decoder 30 may receive such SEI messages, parseand/or decode the information, and pass that information to videopost-processor 31.

In another example, neither the first global offset value nor the secondglobal offset value is signaled in a SEI message. Instead, decoder 30assumes that the values of the first global offset and the second globaloffset is a constant, predetermined, or signaled value that the decoder30 either determines per sequence or receives by external means. Inanother example, video encoder 20 signals the first global offset valuein an SEI message, but the second global offset value is not signaled ina SEI message. Instead, video decoder 30 infers that its value is aconstant, predetermined, or signaled value that decoder 30 eitherdetermines per sequence or received by external means. In a stillfurther example, video encoder 20 signals the second global offset valuein an SEI message, but the first global offset value is not signaled ina SEI message. Instead, video decoder 30 infers that the first globaloffset value is a constant, predetermined, or signaled value thatdecoder 30 either determines per sequence or received by external means.

In some examples, video encoder 20 may signal offset values that arereceived by decoder 30, and are used by decoder 30 to derive otherglobal or local parameters, including both global and local scale andoffset values, as well as partitions of a range of unadjusted values,and partitions of a range of adjusted values.

In some examples, video encoder 20 may signal one or more SEI messagesthat include the number of partitions that the range of inputrepresentation values (i.e., component values) was divided into duringdynamic range adjustment. In one example, the number of partitions maybe constrained to be a power of 2 (i.e. 1, 2, 4, 8, 16, etc.) and thenumber of partitions is signaled as logarithm (e.g. 8 partitions issignaled as 3=log₂ 8). Video decoder 30 may receive such SEI messages,parse and/or decode the information, and pass that information to videopost-processor 31.

In some examples, the number of partitions for the chroma components maybe different from the number of partitions for the luma component. Thenumber of partitions may be constrained to be a power of 2+1 andsignaled as logarithm and rounding towards minus 0. In this way, pixelswith neutral chroma can have their own values and the size of thatpartition can be smaller than the other partitions. In such an example,neutral chroma may refer to values of chroma around the mid-value (e.g.,0 when the chroma values range between −0.5 and 0.5, or between −512 and511 in a 10-bit representation). Constraining the number of partitionsas a power of 2 may enable the encoder 20 to save bits, because encoder20 may be able to represent the log of a value with fewer bits than theactual value for integer values. Constraining the number of partitionsto a power of 2+1 may ensure that at least one partition may bededicated to the neutral chroma values, and in some examples, the widthof the partition corresponding to the neutral chroma values may besmaller than the rest. In other examples, such a partition may be largerthan one or more of the other partitions.

In some examples, decoder 30 may use the signaled number of partitionsto derive other global or local parameters, including both global andlocal scale and offset values, as well as the actual size of thepartitions of a range of unadjusted component values and/or the size ofthe partitions of a range of adjusted component values.

In some examples, encoder 20 may signal one or more SEI messages thatmay include, for each partition, a local scale and local offset valuespecifying a range of the input component values and the correspondingmapped output component values. In some examples, encoder 20 may signalan SEI message that includes the number of bits used by the syntaxelements to signal the scale and offsets. In other examples, encoder 20may signal an SEI message that indicates the number of bits that areused to represent the fractional part of the scale and offsets in thesyntax elements. In other examples, encoder 20 may signal one or moreSEI messages or syntax elements that indicate that the integer part ofthe scale parameters is signaled in a signed representation. In someexamples, the signed representation is two's complement. In otherexamples, the signed representation is signed magnitude representation.Video decoder 30 may receive such SEI messages and/or syntax elements,parse and/or decode the information, and pass that information to videopost-processor 31.

In other examples, encoder 20 may use each offset value successively tofirst compute the range of adjusted component or representation values,and then using the scale value, compute the corresponding range in theunadjusted representation. For example, one offset value may be used tocompute the range of a first partition in the adjusted component usingthe value of a global offset value derived or signalled for the adjustedcomponent, followed by using the scale value and the range of a firstpartition of the adjusted representation to derive the range in thecorresponding partition of the unadjusted representation and with therespective ranges of the first partition of the adjusted and thecorresponding partition of the unadjusted representations, derive arespective value derived for the first partition of the adjusted rangeand the corresponding partition of unadjusted representations thatindicate a boundary of the partitions. Following this, another offsetvalue may be used to compute the range of a second partition in theadjusted component using the boundary value of the first partition inthe adjusted component derived in the previous step, followed by usingthe scale value and the range of a second partition of the adjustedrepresentation to derive the range of the unadjusted representation, andwith the respective ranges of the second partitions of the adjustedrepresentation and corresponding partition of the unadjustedrepresentations, a respective value is derived for the partitions in theadjusted and unadjusted representations that indicate a boundary of therespective representations.

This method is repeated until all the ranges and boundaries are derivedfor all the partitions in the adjusted and unadjusted representations.In another example, encoder 20 may use each offset value successively tofirst compute the range of unadjusted component or representationvalues, and then using the scale value, compute the corresponding rangein the adjusted representation. In other words, the component orrepresentation to which the scale and offset values are applied could beswapped between unadjusted and adjusted representations.

In some examples, the number of bits used by the syntax elements tosignal scale and offset values may depend on the component. In otherexamples, a default number of bits is defined and used when thesenumbers are not explicitly signaled.

In some examples, encoder 20 may signal a syntax element indicatingwhether the length of the partitions of the output representations(i.e., output components) are equal. In such an example, encoder 20might not signal the offset value for one or more partitions. Decoder 30may infer the offset values to be equal in some examples. In anotherexample, decoder 30 may assume the partitions are of equal length andmay not receive a syntax element so indicating. In some examples,decoder 30 may derive the size of each partition from signaled syntaxelements and predefined total dynamical range of the representation.

In other examples, rather than signaling pivot points for each partitionas well as scale and offset values for each partition, video encoder 20may signal one or more SEI messages that indicate derivative or scalevalue for each partition along with the size of one or more or allpartitions. This approach may allow encoder 20 to avoid signaling localoffset values for each partition. Instead, in some examples, encoder 20may be able to signal, in one or more SEI messages, the partition sizeand scale value (or derivative) for one or more partitions. The localoffset value for each partition or partitioning (which may requirehigher accuracy) may be determined or derived by decoder 30.

In some examples, encoder 20 may signal one or more SEI messages thatindicate a mode value that specifies several default values for offsetand scale values for certain partitions. Video decoder 30 may receivesuch SEI messages, parse and/or decode the information, and pass thatinformation to video post-processor 31.

In some examples, encoder 20 may signal one or more SEI messages thatindicate a value defining the persistence of the SEI message such thatthe persistence of a subset of the components may be defined andcomponent scale values of a subset of the components may be updated. Thepersistence of an SEI message indicates the pictures to which the valuessignalled in the instance of the SEI may apply. In some examples, thepersistence of the SEI message is defined such that the values signalledin one instance of SEI messages may apply correspondingly to the allcomponents of the pictures to which the SEI message applies. In otherexamples, the persistence of the SEI message is defined such that thevalues signalled in one instance of the SEI may be indicated to applycorrespondingly to a subset of the components wherein the components towhich the values in the instance of the SEI does not apply may eitherhave no values applicable or may have values applicable that aresignalled in another instance of the SEI message. Video decoder 30 mayreceive such SEI messages, parse and/or decode the information, and passthat information to video post-processor 31.

In some examples, encoder 20 may signal one or more SEI messages thatinclude syntax elements indicating the post-processing steps to beperformed to the decoded output. Each syntax element may be associatedwith a particular process (e.g. scaling components, color transforms,up-sampling/down-sampling filters, etc.) and each value of the syntaxelement may specify that a particular set of parameters associated withthe process be used. In some examples, the parameters associated withthe process are signaled by video encoder 20 using SEI messages that arepart of the bitstream or as metadata that may be transmitted throughother means. Video decoder 30 may receive such SEI messages, parseand/or decode the information, and pass that information to videopost-processor 31.

In some examples, encoder 20 may signal syntax elements or one or moreSEI messages that may be used for describing and/or constructing apiece-wise linear model function for mapping input representations(i.e., input component values) to output representations (i.e., outputcomponent values). Video decoder 30 may receive such SEI messages, parseand/or decode the information, and pass that information to videopost-processor 31. In other examples, predefined assumptions may be usedfor describing and/or constructing a piece-wise linear model functionfor mapping input representations to the output representation.

In some examples, encoder 20 may signal one or more SEI messages thatmay include one or more syntax elements indicating that the scale andoffset parameters signaled in the SEI message represent the variation ofthe scale to be applied to a first component as a function of differentvalues of a second component.

In some examples, encoder 20 may signal one or more SEI messagesindicating offset parameters that are to be or may be applied along withthe scale on a first component as a function of different values of asecond component. In some examples, encoder 20 may signal one or moreSEI messages that may include one or more additional syntax elementsthat indicating offset parameters that are to be or may be applied alongwith the scale on a first component as a function of different values ofa second component. Video decoder 30 may receive such SEI messages,parse and/or decode the information, and pass that information to videopost-processor 31.

In some examples, encoder 20 may signal one or more SEI messagesincluding a first syntax element that indicates a first set ofelectro-optical transfer function characteristics such that the signaledscale, offset and other dynamic range adjustment parameters the SEImessage are applied when the electro-optical transfer functioncharacteristics used on the decoder-side are similar to that first setof electro-optical transfer function characteristics.

In another example, encoder 20 may signal one or more SEI messagesindicating that the signaled offset, scale and other dynamic rangeparameters in the SEI message(s) are to be applied for bestreconstruction of the HDR output when the first set of electro-opticaltransfer function characteristics, or those with similarcharacteristics, are used by the decoder 30. Video decoder 30 mayreceive such SEI messages, parse and/or decode the information, and passthat information to video post-processor 31.

In another example, encoder 20 may signal one or more SEI messagesindicating that a first set of opto-electronic transfer functioncharacteristics, and the signaled scale, offset and other dynamic rangeadjustment parameters are applied on by decoder 30 when thecorresponding inverse electro-optical transfer function characteristicsare applied at the decoder side. Video decoder 30 may receive such SEImessages, parse and/or decode the information, and pass that informationto video post-processor 31.

In other examples, encoder 20 may signal a condition such that when morethan one SEI message is present indicating different set ofelectro-optical/opto-electronic characteristics and applicable thecurrent picture, only one SEI message is applied. The encoder may signaldifferent set of electro-optical/opto-electronic characteristics tosatisfy different types of decoders, or decoders with differentcapabilities. For example, some displays at the decoder side may applythe PT EOTF to convert the coded component values in appropriate domainto linear light, whereas other displays, e.g. legacy displays, may applythe gamma EOTF to convert to linear light. Each SEI with a particularcharacteristic that the encoder sends may be appropriate or beneficialfor certain types of displays and not for other types of displays, e.g.an SEI message with PQ EOTF characteristics may be suitable for displaysthat apply PQ EOTF to convert the coded video to linear light. Thedecoder 30 determines which SEI message is to be applied, and makes sucha choice based on the application standard, based on the end-userdevice, based on a signal received, or based on another indicationreceived through external means. For example, decoder 30 may determinethat the first syntax element in a first SEI message that applies to acurrent picture indicates that the SEI message is to be applied with theinverse of PQ OETF and the first syntax element in a second SEI messagethat applies to a current picture indicates that the SEI message is tobe applied with another transfer function (such as BBC, or PH), thedecoder 30 or end-user device may choose to apply the parameters in thefirst SEI message because the device uses PQ EOTF. In some examples, anapplication standard to which the decoder conforms to may specify thatan SEI message with a particular set of characteristics is to be used.

In other examples, encoder 20 may signal an SEI message that carries theparameters corresponding to multiple sets of transfer characteristics.In other examples, encoder 20 may signal different SEI messages for thatpurpose. Video decoder 30 may receive such SEI messages, parse and/ordecode the information, and pass that information to videopost-processor 31

In some examples, encoder 20 may signal one or more SEI messages thatinclude a syntax element indicating the applicability of the SEImessage. The applicability of the SEI message may include, but is notlimited to (1) the components to which the scales and offsets apply, (2)the position at which the component scaling is applied, and/or (3)whether additional scaling parameters are signaled.

As described, encoder 20 may signal one or more SEI messages thatinclude a syntax element indicating the components to which the scalesand offsets apply. The following lists several examples of such anapplication. For example, one value of the syntax element could indicatethat signaled parameters for the first component index are to be appliedto the RGB components. Another value may indicate that the signaledparameters for the first component index is to be applied to lumacomponent, and those for the second and third indices are to be appliedto the Cb and Cr components. Another value may indicate that thesignaled parameters for the first component index is to be applied to R,G and B components, and those for the second and third indices are to beapplied to the Cb and Cr components. Another value may indicate thatsignaled parameters for first three indices are applied to luma, Cb andCr components, and that corresponding to the remaining indices areapplied for color correction. Video decoder 30 may receive such SEImessages, parse and/or decode the information, and pass that informationto video post-processor 31.

Also as described, encoder 20 may signal one or more SEI messagesincluding a syntax element indicating the position at which thecomponent scaling is applied.

Several processes occur on the decoder-side, after decoding of thevideo, and in the video post-processor 31. Signaling of syntax elementindicating the position at which the process associated with the SEI isto be applied, in other words indication of any subset of the precedingor succeeding operations of the process associated with using theinformation in the SEI, would be helpful to the video decoder 30 or thevideo post-processor 31 to process the video. For example, such a syntaxelement could indicate the position at which the component scaling isapplied, for example to YCbCr components before or after upsampling. Inanother example, the syntax element could indicate that the componentscaling is applied before the quantization no the decoder side. Videodecoder 30 may receive such SEI messages, parse and/or decode theinformation, and pass that information to video post-processor 31.

Also as described, encoder 20 may signal one or more SEI messages thatinclude a syntax element indicating whether an additional set of scalingand parameters, e.g. for color correction, are signaled. The additionalset of parameters could be used for color correction to map the colorcomponents to fit a particular color gamut, or for correction ofcomponent values when a different transfer function is applied than thatindicated by the transfer_characteristics syntax element in the VUI.

In other examples, encoder 20 may signal different syntax elements toindicate the above aspects; e.g. one syntax element to indicate whichcomponent(s) the SEI applies to, one syntax element to indicate whetherit applies to HDR-compatible of SDR-compatible content, and one syntaxelement to indicate the position(s) where the component scaling SEImessage is to be applied.

When the number of components to which the component scaling SEI messageparameters are applied is more than one, encoder 20 may signal one ormore SEI messages that include a syntax element indicating thatapplication of scale and offset parameters may be done sequentiallybased on the index of the component. For example, the mapping based onthe scale and offset parameters of the first component may be applied,and then the mapping of the second component, which for example usesscale and offset signaled for the second component, may depend on thevalues of the first component. In some examples, this is indicated by,for example, by syntax element specifying that the mapped values of thefirst component should be used. Video decoder 30 may receive such SEImessages, parse and/or decode the information, and pass that informationto video post-processor 31.

In another example, video encoder 20 may constrain the values signaledin one or more SEI messages, or in the bitstream, in such a way that anHDR10 receiver can decode and show a viewable HDR video even if the SEIpost-processing is not applied. The SEI message(s) may include a syntaxelement to indicate that this is the case (e.g., that the bitstream isan HDR10 backward compatible bitstream).

This section includes several examples that use techniques disclosed inaccordance with one or more aspects of the present disclosure.

Example 1

In this example 1, the component scaling function is signaled as alook-up table and the number of bits used to signal the points definingthe look up table are also signaled. For sample values that do not haveexplicit points signaled, the value is interpolated based on theneighboring pivot points.

Syntax of the Component Scaling SEI Message

De- scrip- tor component_scale_info( payloadSize ) { comp_scale_id ue(v)comp_scale_cancel_flag u(1) if( !comp_scale_cancel_flag ) {comp_scale_persistence_flag u(1) comp_scale_num_comps_minus1 ue(v)comp_scale_input_bit_depth ue(v) comp_scale_output_bit_depth ue(v) for(c = 0; c <= comp_scale_num_comps_minus1; c++ ) {comp_scale_num_points_minus1[ c ] ue(v) for( i = 0; i <=comp_scale_num_points_minus1[ c ]; i++ ) { comp_scale_input_point[ c ][i ] u(v) comp_scale_output_point[ c ][ i ] u(v) } } } }

Semantics of the Component Scaling SEI Message

The component scaling SEI message provides information to performscaling operations on the various components of the decoded pictures.The colour space and the components on which the scaling operationsshould be performed are determined by the value of the syntax elementssignalled in the SEI message.

comp_scale_id contains an identifying number that may be used toidentify the purpose of the component scaling SEI message. The value ofcomp_scale_id shall be in the range of 0 to 2³²−2, inclusive. The valueof comp_scale_id may be used to specify the colour space at which thecomponent scaling SEI message, or whether the component scaling SEImessage is applied in the linear or the non-linear domain.

Values of comp_scale_id from 0 to 255, inclusive, and from 512 to 2³¹−1,inclusive, may be used as determined by the application. Values ofcomp_scale_id from 256 to 511, inclusive, and from 2³¹ to 2³²−2,inclusive, are reserved for future use by ITU-T|ISO/IEC. Decoders shallignore all component scale information SEI messages containing a valueof comp_scale_id in the range of 256 to 511, inclusive, or in the rangeof 2³¹ to 2³²−2, inclusive, and bitstreams shall not contain suchvalues.

NOTE 1—The comp_scale_id can be used to support component scalingprocesses that are suitable for different display scenarios. Forexample, different values of comp_scale_id may correspond to differentdisplay bit depths or different colour spaces in which the scaling isapplied.

Alternatively, the comp_scale_id may also be used to identify whetherthe scaling is performed for compatibility to certain types of displaysor decoder, e.g. HDR, SDR. comp_scale_cancel_flag equal to 1 indicatesthat the component scaling information SEI message cancels thepersistence of any previous component information SEI messages in outputorder that applies to the current layer. comp_scale_cancel_flag equal to0 indicates that component scaling information follows.

comp_scale_persistence_flag specifies the persistence of the componentscaling information SEI message for the current layer.

comp_scale_persistence_flag equal to 0 specifies that the componentscaling information applies to the current decoded picture only.

Let picA be the current picture. comp_scale_persistence_flag equal to 1specifies that the component scaling information persists for thecurrent layer in output order until any of the following conditions aretrue:

-   -   A new CLVS of the current layer begins.    -   The bitstream ends.    -   A picture picB in the current layer in an access unit containing        a component scaling information SEI message with the same value        of comp_scale_id and applicable to the current layer is output        for which PicOrderCnt(picB) is greater than PicOrderCnt(picA),        where PicOrderCnt(picB) and PicOrderCnt(picA) are the        PicOrderCntVal values of picB and picA, respectively,        immediately after the invocation of the decoding process for        picture order count for picB.

comp_scale_num_comps_minus1 plus 1 specifies the number of componentsfor which the component scaling function is specified.comp_scale_num_comps_minus1 shall be in the range of 0 to 2, inclusive.

When comp_scale_num_comps_minus1 is less than 2 and the componentscaling parameters of the c-th component is not signalled, are inferredto be equal to those of the (c−1)-th component.

Alternatively, when comp_scale_num_comps_minus1 is less than 2, and thecomponent scaling parameters of the c-th component is not signalled, thecomponent scaling parameters of the c-th component are inferred to beequal to default values such that effectively there is no scaling ofthat component.

Alternatively, the inference of the component scaling parameters may bespecified based on the colour space on which the SEI message is applied.

-   -   When the colour space is YCbCr, and comp_scale_num_comps_minus1        is equal to 1, the component scaling parameters apply to both Cb        and Cr components.    -   When the colour space is YCbCr, and comp_scale_num_comps_minus1        is equal to 2, the first and second component scaling parameters        apply to Cb and Cr components.

In one alternative, the different inference is specified based on thevalue of comp_scale_id or on the basis of an explicit syntax element.

Alternatively, a constraint is added as follows:

It is constraint for bitstream conformance that the value ofcomp_scale_num_comps_minus 1 shall be the same for all the componentscaling SEI message with a given value of comp_scale_id within a CLVS.comp_scale_input_bit_depth_minus8 plus 8 specifies the number of bitsused to signal the syntax element comp_scale_input_point[c][i]. Thevalue of comp_scale_input_bit_depth_minus8 shall be in the range of 0 to8, inclusive.

When component scaling SEI message is applied to an input that is in anormalized floating point representation in the range 0.0 to 1.0, theSEI message refers to the hypothetical result of a quantizationoperation performed to convert the input video to a converted videorepresentation with bit depth equal tocolour_remap_input_bit_depth_minus8+8.

When component scaling SEI message is applied to a input that has a bitdepth not equal to the comp_scale_input_bit_depth_minus8+8, the SEImessage refers to the hypothetical result of a transcoding operationperformed to convert the input video representation to a converted videorepresentation with bit depth equal tocolour_remap_input_bit_depth_minus8+8.comp_scale_output_bit_depth_minus8 plus 8 specifies the number of bitsused to signal the syntax element comp_scale_output_point[c][i]. Thevalue of comp_scale_output_bit_depth_minus8 shall be in the range of 0to 8, inclusive.

When component scaling SEI message is applied to an input that is infloating point representation, the SEI message refers to thehypothetical result of an inverse quantization operation performed toconvert the video representation with a bit depth equal tocolour_remap_output_bit_depth_minus8+8 that is obtained after processingof the component scaling SEI message to a floating point representationin the range 0.0 to 1.0.

Alternatively, the number of bits used to signalcomp_scale_input_point[c][i] and comp_scale_output_point[c][i] aresignalled as comp_scale_input_bit_depth and comp_scale_output_bit_depth,respectively, or in other words without subtracting 8.comp_scale_num_points_minus1[c] plus 1 specifies the number of pivotpoints used to define the component scaling function.comp_scale_num_points_minus1[c] shall be in the range of 0 to(1<<Min(comp_scale_input bit_depth_minus8+8,comp_scale_output_bit_depth_minus8+8))−1, inclusive.

comp_scale_input_point[c][i] specifies the i-th pivot point of the c-thcomponent of the input picture. The value ofcomp_scale_input_point[c][i] shall be in the range of 0 to(1<<comp_scale_input bit_depth_minus8 [c]+8)−1, inclusive. The value ofcomp_scale_input_point[c][i] shall be greater than or equal to the valueof comp_scale_input_point[c][i−1], for i in the range of 1 tocomp_scale_points_minus1[c], inclusive.

comp_scale_output_point[c][i] specifies the i-th pivot point of the c-thcomponent of the output picture. The value ofcomp_scale_output_point[c][i] shall be in the range of 1 to(1<<comp_scale_output bit_depth_minus8[c]+8)−1, inclusive. The value ofcomp_scale_output_point[c][i] shall be greater than or equal to thevalue of comp_scale_output_point[c][i−1], for i in the range of 1 tocomp_scale_points_minus1[c], inclusive.

The process of mapping an input signal representation x and an outputsignal representation y, where the sample values for both input andoutput are in the range of 0 to(1<<comp_scale_input_bit_depth_minus8[c]+8)−1, inclusive, and 0 to(1<<comp_scale_output_bit_depth_minus8[c]+8)−1, inclusive, respectively,is specified as follows:

if( x <= comp_scale_input_point[ c ][ 0 ] ) y = comp_scale_output_point[c ][ 0 ] else if( x > comp_scale_input_point[ c ][comp_scale_input_point_minus1[ c ] ] ) y = comp_scale_output_point[ c ][comp_scale_output_point_minus1[ c ] ] else for( i = 1; i <=comp_scale_output_point_minus1[ c ]; i++ ) if( comp_scale_input_point[ i− 1 ] < x && x <= comp_scale_input_point[ i ] ) y = ( (comp_scale_output_point[ c ][ i ] − comp_scale_output_point[ c ][ i − 1] ) ÷ ( comp_scale_input_point[ c ][ i ] − comp_scale_input_point[ c ][i − 1 ] ) ) * ( x − comp_scale_input_point[ c ][ i − 1 ] ) +  (comp_scale_output_point[ c ][ i − 1 ] )

In one alternative, input and output pivot pointscomp_scale_input_point[c][i] and comp_scale_output_point[c][i] are codedas difference of adjacent values; e.g., delta_comp_scale_input_point[ ][] and delta_comp_scale_output_point[ ][ ], and the syntax elements arecoded using exponential Golomb codes.

In another alternative, the process of mapping an input and outputrepresentation value is specified by other interpolation methodsincluding, but not limited to, splines and cubic interpolation.

Example 2

This Example 2 shows a different syntax structure compared to the SEIsyntax structure described in Example 1. In this syntax structure, themapping function is described in terms of scales and offsets instead ofpivot points.

Syntax of the Component Scaling SEI Message

De- scriptor component_scale_info( payloadSize ) { comp_scale_id ue(v)comp_scale_cancel_flag u(1) if( !comp_scale_cancel_flag ) {comp_scale_persistence_flag u(1) comp_scale_num_comps ue(v)comp_scale_input_bit_depth ue(v) comp_scale_output_bit_depth ue(v)comp_scale_bit_depth_scale_val ue(v) comp_scale_log2_denom_scale_value(v) for( c = 0; c < comp_scale_num_comps; c++ ) {comp_scale_num_points_minus1[ c ] ue(v)comp_scale_global_offset_input_val[ c ] u(v)comp_scale_global_offset_output_val[ c ] u(v) for( i = 0; i <comp_scale_num_points_minus1[ c ]; i++ ) { comp_scale_offset_val[ c ][ i] u(v) comp_scale_val[ c ][ i ] u(v) } } } }

comp_scale_bit_depth_scale_val specifies the number of bits used tosignal the syntax element comp_scale_val[c][i]. The value ofcomp_scale_bit_depth_scale_val shall be in the range of 0 to 24,inclusive.

comp_scale_log 2_denom_scale_val specifies the base 2 denominator of thescale value. The value of comp_scale_log 2_denom_scale_val shall be inthe range of 0 to 16, inclusive.

comp_scale_global_offset_input_val[c] plus 1 specifies the input samplevalue below which all the input representation values are clipped toCompScaleOffsetOutputVal[c][0]. used to define the component scalingfunction. comp_scale_num_points_minus1[c] shall be in the range of 0 to(1<<comp_scale_input_bit_depth)−1, inclusive. The number of bits used torepresent comp_scale_global_offset_input_val[c] iscomp_scale_input_bit_depth. comp_scale_global_offset_output_val[c] plus1 specifies the output sample value to which all the inputrepresentation values below comp_scale_global_offset_input_val[c] are tobe clipped. comp_scale_num_points_minus1[c] shall be in the range of 0to (1<<comp_scale_output_bit_depth)−1, inclusive. The number of bitsused to represent comp_scale_global_offset_output val[c] iscomp_scale_output_bit_depth. comp_scale_num_points_minus1[c] plus 1specifies the number of pivot points used to define the componentscaling function. comp_scale_num_points_minus1[c] shall be in the rangeof 0 to (1<<Min(comp_scale_input_bit_depth,comp_scale_output_bit_depth)−1, inclusive.

The process of mapping an input signal representation x and an outputsignal representation y, where the sample values for both inputrepresentation is in the range of 0 to(1<<comp_scale_input_bit_depth)−1, inclusive, and output representationis in the range of and 0 to (1<<comp_scale_output_bit_depth)−1,inclusive, is specified as follows:

if( x <= CompScaleOffsetInputVal[ c ][ 0 ] ) y =CompScaleOffsetOutputVal[ c ][ 0 ] else if( x > CompScaleOffsetInputVal[c ][ comp_scale_output_point_minus1 ] ) y = CompScaleOffsetOutputVal[ c][ comp_scale_output_point_minus1 ] else for( i = 1; i <=comp_scale_output_point_minus1; i++ ) if( CompScaleOffsetInputVal[ i − 1] < x && x <= CompScaleOffsetInputVal[ i ] ) y = (x −CompScaleOffsetInputVal[ i − 1 ] * ( comp_scale_val[ c ][ i ] +CompScaleOffsetOutputVal[ c ][ i ]

comp_scale_offset_val[c][i] specifies the offset value of the i-thsample value region of the c-th component. The number of bits used torepresent comp_scale_offset_val[c] is equal tocomp_scale_input_bit_depth.

comp_scale_val[c][i] specifies the scale value of the i-th sample valueregion point of the c-th component. The number of bits used to representcomp_scale_val[c] is equal to comp_scale_bit_depth_scale_val.

The variables CompScaleOffsetOutputVal[c][i] andCompScaleOffsetInputVal[c][i] for i in the range of 0 tocomp_scale_num_points_minus1[c], inclusive, is derived as follows:

roundingOffset = (comp_scale_log2_denom_scale_val = = 0 ) ? 0 : (1 <<comp_scale_log2_denom_scale_val − 1) for( i = 0; i <=comp_scale_num_points_minus1[ c ]; i++ ) if( i = = 0 )CompScaleOffsetOutputVal[ c ][ i ] =comp_scale_global_offset_output_val[ c ] CompScaleOffsetInputVal[ c ][ i] = comp_scale_global_offset_input_val[ c ] elseCompScaleOffsetOutputVal[ c ][ i ] = CompScaleOffsetOutputVal[ c ][ i −1 ] + (comp_scale_offset_val[ c ][ i − 1 ] □ comp_scale_val[ c ][ i − 1] + roundingOffset ) >> comp_scale_log2_denom_scale_valCompScaleOffsetInputVal[ c ][ i ] = CompScaleOffsetInputVal[ c ][ i − 1] + comp_scale_offset_val[ c ][ i − 1 ]

In one alternative, comp_scale_offset_val[c][i] is used to directlycalculate CompScaleOffsetOutputVal[ ][i] and indirectly calculateCompScaleOffsetInputVal[ ][i] for i in the range of 0 tocomp_scale_num_points_minus1[c] as follows:

for( i = 0; i < comp_scale_num_points_minus1[ c ]; i++ )     if( i == 0)       CompScaleOffsetOutputVal[ c ][ i ] =comp_scale_global_offset_output_val[ c ]       CompScaleOffsetInputVal[c ][ i ] = comp_scale_global_offset_input_val[ c ]     else      CompScaleOffsetInputVal[ c ][ i ] = CompScaleOffsetInputVal[ c ][i − 1 ] +               (comp_scale_offset_val[ c ][ i − 1 ] *comp_scale_val[ c ][ i − 1 ]               + roundingOffset ) >>comp_scale_log2_denom_scale_val )       CompScaleOffsetOutputVal[ c ][ i] = CompScaleOffsetOutputVal[ c ][ i − 1 ] +                  comp_scale_offset_val[ c ][ i − 1 ]

In one alternative, comp_scale_offset_val[c][i] for i in the range of 0to comp_scale_num_points_minus1[c], inclusive, are not signaled, and thevalues of comp_scale_offset_val[c][i] are derived based oncomp_scale_num_points_minus1[c] equally spaced intervals for which thescale is specified. The value of comp_scale_offset_val[c][i] for i inthe range of 0 to comp_scale_num_points_minus1[c]−1, inclusive, isderived as follows:

comp_scale_offset_val[ c ][ i ] =       ( (1 <<comp_scale_output_bit_depth ) −      comp_scale_global_offset_output_val[ c ] ) ÷(comp_scale_num_points_minus1[ c ])

In another alternative, comp_scale_offset_val[c][i] for i in the rangeof 0 to comp_scale_num_points_minus 1[c] is calculated as follows:

comp_scale_offset_val[ c ][ i ] = (1 << comp_scale_output_bit_depth) ÷(comp_scale_num_points_minus1[ c ] )

In one alternative, instead of signalingcomp_scale_num_points_minus1[c], the number of pivot points is signaledusing log 2_comp_scale_num_points[c], where (1<<log2_comp_scale_num_points[c]) specifies the number of pivot points for thec-th component.

Alternatively, each of comp_scale_offset_val[c][ ] andcomp_scale_val[c][ ] is signaled as floating point numbers, or as twosyntax elements with exponent and mantissa.

In another alternative, signaling of comp_scale_val[c][i] is replaced bycomp_scale_output_point[c][i].

The semantics of rest of the syntax elements are similar to thosedescribed in Example 1.

Example 3

This method described in Example 3 is similar to one of the alternativesdescribed in Example 2, with the exception that the component scalingfunctions are allowed to be updated independently.

Syntax of the Component Scaling SEI Message

De- scrip- tor component_scale_info( payloadSize ) { comp_scale_id ue(v)comp_scale_cancel_flag u(1) if( !comp_scale_cancel_flag ) {comp_scale_persistence_flag u(1) comp_scale_num_comps ue(v)comp_scale_input_bit_depth ue(v) comp_scale_output_bit_depth ue(v) for(c = 0; c < comp_scale_num_comps; c++ ) {comp_scale_persist_component_flag[ c ] u(1) if(!comp_scale_persist_component_flag[ c ] ) comp_scale_num_scale_regions[c ] ue(v) comp_scale_global_offset_input_val[ c ] u(v)comp_scale_global_offset_output_val[ c ] u(v) for( i = 0; i <comp_scale_num_scale_regions[ c ]; i++ ) { comp_scale_offset_val[ c ][ i] u(v) comp_scale_val[ c ][ i ] u(v) } } } } }

Semantics of the Component Scaling SEI Message

The semantics is similar to Example 2, except for the following syntaxelements. comp_scale_num_scale_regions[c] specifies the number ofregions for which the syntax element comp_scale_val[c][i] is signalledfor the c—the component. comp_scale_num_scale_regions[c] shall be in therange of 0 to (1<<comp_scale_input_bit_depth)−1, inclusive.

comp_scale_persist_component_flag[c] equal to 0 specifies that componentscaling parameters for the c-th component are explicitly signalled inthe SEI message. comp_scale_persist_component flag[c] equal to 1specifies that component scaling parameters for the c-th component arenot explicitly signalled in the SEI message, and it persists from thecomponent scaling parameters of the c-th component of the componentscaling SEI message that applies to previous picture, in output order.

It is a requirement of bitstream conformance that when the componentscaling SEI message is present in an IRAP access unit, the value ofcomp_scale_persist_component_flag[c], when present, shall be equal to 0.

Alternatively, the following condition is added:

It is a requirement of bitstream conformance that when the componentscaling SEI message is present in an access unit that is not an IRAPaccess unit and comp_scale_persist_component_flag[c] is equal to 1, thenthere is at least one picture that precedes the current picture inoutput order and succeeds, in output order, the previous IRAP picture indecoding order, inclusive, such that the one picture is associated witha component scaling SEI message with comp_scale_persistence_flag equalto 1.

comp_scale_persistence_flag specifies the persistence of the componentscaling information SEI message for the current layer.

comp_scale_persistence_flag equal to 0 specifies that the componentscaling information applies to the current decoded picture only.

Let picA be the current picture comp_scale_persistence_flag equal to 1specifies that the component scaling information of the c-th componentpersists for the current layer in output order until any of thefollowing conditions are true:

-   -   A new CLVS of the current layer begins.    -   The bitstream ends.    -   A picture picB in the current layer in an access unit containing        a component scaling information SEI message with the same value        of comp_scale_id and comp_scale_persist_component_flag[c] equal        to 0, and applicable to the current layer is output for which        PicOrderCnt(picB) is greater than PicOrderCnt(picA), where        PicOrderCnt(picB) and PicOrderCnt(picA) are the PicOrderCntVal        values of picB and picA, respectively, immediately after the        invocation of the decoding process for picture order count for        picB.

Example 4

In this Example 4, a different method to signal the scale regions isdisclosed.

Changes to Component Scaling SEI Message Syntax

De- scrip- tor component_scale_info( payloadSize ) { comp_scale_id ue(v)comp_scale_cancel_flag u(1) if( !comp_scale_cancel_flag ) {comp_scale_persistence_flag u(1) comp_scale_num_comps ue(v)comp_scale_input_bit_depth ue(v) comp_scale_output_bit_depth ue(v) for(c = 0; c < comp_scale_num_comps; c++ ) {comp_scale_persist_component_flag[ c ] u(1) if(!comp_scale_persist_component_flag[ c ] )comp_scale_global_offset_input_val[ c ] u(v)comp_scale_global_offset_output_val[ c ] u(v)comp_scale_num_scale_regions[ c ] ue(v) for( i = 0; i <comp_scale_num_scale_regions[ c ]; i++ ) { comp_scale_offset_begin_val[c ][ i ] u(v) comp_scale_offset_end_val[ c ][ i ] u(v) comp_scale_val[ c][ i ] u(v) } } } } }

Changes to Component Scaling SEI Message Semantics

The semantics of the syntax elements are similar to those described inprevious examples, except for the following:

comp_scale_offset_begin_val[c][i] specifies the beginning of the samplevalue range for which the scale value comp_scale_val[c][i] isapplicable. The number of bits used to representcomp_scale_offset_begin_val[c] is equal to comp_scale_input_bit_depth.

comp_scale_offset_end_val[c][i] specifies the end of the sample valuerange for which the scale value comp_scale_val[c][i] is applicable. Thenumber of bits used to represent comp_scale_offset_end val[c] is equalto comp_scale_input_bit_depth. For regions that are not explicitlyspecified by comp_scale_offset_begin val and comp_scale_offset_end_val,the comp_scale_value[c][i] for those regions is inferred to be equal to0.

Alternatively, comp_scale_offset_end_val[c][i] is not signaled andinstead the difference between comp_scale_offset_end val[c][i] andcomp_scale_offset_begin_val[c][i] is signaled, and the value ofcomp_scale_offset_end_val[c][i] derived at the decoder-side.

In another alternative, the total number of regions in to which theoutput sample range is split is specified, and the number of regions issignaled for which the scale regions are explicitly signaled.

... u(v) comp_scale_global_offset_output_val[ c ] u(v)comp_scale_tot_scale_regions[ c ] ue(v) comp_scale_num_scale_regions[ c] ue(v) for( i = 0; i < comp_scale_num_scale_regions[ c ]; i++ ) {comp_scale_region_idx[ c ][ i ] u(v) comp_scale_val[ c ][ i ] u(v) } ...

comp_scale_tot_scale_regions[c] specifies the total number of equallength sample value ranges in to which the sample values are split. Thenumber of bits used to represent comp_scale tot_scale_regions[c] isequal to comp_scale_input_bit_depth. In one alternative, the comp_scaletot_scale_regions[c] sample value ranges may not be exactly equal inlength but very nearly equal to account for the integer accuracy of theregion lengths.

comp_scale_region_idx[c][i] specifies the index of the sample valuerange for which the scale value comp_scale_val[c][i] is applied. Thelength of the syntax element comp_scale_region_idx[c] is Ceil(Log2(comp_scale tot scale regions[c])) bits.

Alternatives

Alternatively, region around the chroma neutral (511 for 10-bit data)have smaller size, p.e., half the size of the other regions.

Example 5 Syntax of the Component Scale SEI Message

De- scrip- tor component_scale_info( payloadSize ) { comp_scale_id ue(v)comp_scale_cancel_flag u(1) if( !comp_scale_cancel_flag ) {comp_scale_persistence_flag u(1) comp_scale_scale_bit_depth u(4)comp_scale_offset_bit_depth u(4) comp_scale_scale_frac_bit_depth u(4)comp_scale_offset_frac_bit_depth u(4) comp_scale_num_comps_minus1 ue(v)for( c = 0; c <= comp_scale_num_comps_minus1; c++ ) {comp_scale_num_ranges[ c ] ue(v) comp_scale_equal_ranges_flag[ c ] u(1)comp_scale_global_offset_val[ c ] u(v) for( i = 0; i <=comp_scale_num_ranges[ c ]; i++ ) comp_scale_scale_val[ c ][ i ] u(v)if( !comp_scale_equal_ranges[ c ] ) u(v) for( i = 0; i <=comp_scale_num_ranges[ c ]; i++ ) comp_scale_offset_val[ c ][ i ] u(v) }}

Semantics of the Component Scale SEI Message

The component scaling SEI message provides information to performscaling operations on the various components of the decoded pictures.The colour space and the components on which the scaling operationsshould be performed are determined by the value of the syntax elementssignalled in the SEI message.

comp_scale_id contains an identifying number that may be used toidentify the purpose of the component scaling SEI message. The value ofcomp_scale_id shall be in the range of 0 to 2³²−2, inclusive. The valueof comp_scale_id may be used to specify the colour space at which thecomponent scaling SEI message, or whether the component scaling SEImessage is applied in the linear or the non-linear domain.

In some examples, comp_scale_id can specify the configuration of the HDRreconstruction process. In some examples, particular value ofcomp_scale_id may be associated with signaling of scaling parameters for3 components. The scaling of the first components to be applied tosamples of R′, G′, B′ color space, and parameters of following 2components are applied for scaling of Cr and Cb.

For yet another comp_scale_id value, hdr reconstruction process canutilize parameters for 3 components, and scaling is applied to samplesof Luma, Cr and Cb color components.

In yet another comp_scale_id value, hdr reconstruction process canutilize signaling for 4 components, 3 of which to be applied to Luma, Crand Cb scaling, and 4th component to bring parameters of colorcorrection.

In some examples, certain range of comp_scale_id values may beassociated with HDR reconstruction conducted in SDR-backward compatibleconfiguration, whereas another range of comp_scale_id values may beassociated with HDR reconstruction conducted to non-backward compatibleconfiguration.

Values of comp_scale_id from 0 to 255, inclusive, and from 512 to 2³¹−1,inclusive, may be used as determined by the application. Values ofcomp_scale_id from 256 to 511, inclusive, and from 2³¹ to 2³²−2,inclusive, are reserved for future use by ITU-T I ISO/IEC. Decodersshall ignore all component scale information SEI messages containing avalue of comp_scale_id in the range of 256 to 511, inclusive, or in therange of 2³¹ to 2³²−2, inclusive, and bitstreams shall not contain suchvalues.

NOTE 1—The comp_scale_id can be used to support component scalingprocesses that are suitable for different display scenarios. Forexample, different values of comp_scale_id may correspond to differentdisplay bit depths or different colour spaces in which the scaling isapplied.

Alternatively, the comp_scale_id may also be used to identify whetherthe scaling is performed for compatibility to certain types of displaysor decoder, e.g. HDR, SDR.

comp_scale_cancel_flag equal to 1 indicates that the component scalinginformation SEI message cancels the persistence of any previouscomponent information SEI messages in output order that applies to thecurrent layer. comp_scale_cancel_flag equal to 0 indicates thatcomponent scaling information follows.

comp_scale_persistence_flag specifies the persistence of the componentscaling information SEI message for the current layer.

comp_scale_persistence_flag equal to 0 specifies that the componentscaling information applies to the current decoded picture only.

Let picA be the current picture. comp_scale_persistence_flag equal to 1specifies that the component scaling information persists for thecurrent layer in output order until any of the following conditions aretrue:

-   -   A new CLVS of the current layer begins.    -   The bitstream ends.    -   A picture picB in the current layer in an access unit containing        a component scaling information SEI message with the same value        of comp_scale_id and applicable to the current layer is output        for which PicOrderCnt(picB) is greater than PicOrderCnt(picA),        where PicOrderCnt(picB) and PicOrderCnt(picA) are the        PicOrderCntVal values of picB and picA, respectively,        immediately after the invocation of the decoding process for        picture order count for picB.

comp_scale_scale_bit_depth specifies the number of bits used to signalthe syntax element comp_scale_scale_val[c][i]. The value ofcomp_scale_scale_bit_depth shall be in the range of 0 to 15, inclusive.

comp_scale_offset bit_depth specifies the number of bits used to signalthe syntax elements comp_scale_global_offset_val[c] andcomp_scale_offset_val[c][i]. The value of comp_scale_offset_bit_depthshall be in the range of 0 to 15, inclusive.comp_scale_scale_frac_bit_depth specifies the number of LSBs used toindicate the fractional part of the scale parameter of the i-thpartition of the c-th component. The value ofcomp_scale_scale_frac_bit_depth shall be in the range of 0 to 15,inclusive. The value of comp_scale_scale_frac_bit_depth shall be lessthan or equal to the value of comp_scale_scale_bit depth.

comp_scale_offset_frac_bit_depth specifies the number of LSBs used toindicate the fractional part of the offset parameter of the i-thpartition of the c-th component and global offset of the c-th component.The value of comp_scale_offset_frac_bit_depth shall be in the range of 0to 15, inclusive. The value of comp_scale_offset frac_bit_depth shall beless than or equal to the value of comp_scale_offset_bit_depth.

comp_scale_num_comps_minus1 plus 1 specifies the number of componentsfor which the component scaling function is specified.comp_scale_num_comps_minus1 shall be in the range of 0 to 2, inclusive.

comp_scale_num_ranges[c] specifies the number of ranges in to which theoutput sample range is partitioned in to. The value ofcomp_scale_num_ranges[c] shall be in the range of 0 to 63, inclusive.

comp_scale_equal_ranges_flag[c] equal to 1 indicates that that outputsample range is partitioned into comp_scale_num_ranges[c] nearly equalpartitions, and the partition widths are not explicitly signalled.comp_scale_equal_ranges_flag[c] equal to 0 indicates that that outputsample range may be partitioned into comp_scale_num_ranges[c] partitionsnot all of which are of the same size, and the partitions widths areexplicitly signalled.

comp_scale_global_offset_val[c] is used to derive the offset value thatis used to map the smallest value of the valid input data range for thec-th component. The length of comp_scale_global_offset_val[c] iscomp_scale_offset_bit_depth bits. comp_scale_scale_val[c][i] is used toderive the offset value that is used to derive the width of the of thei-th partition of the c-th component. The length ofcomp_scale_global_offset_val[c] is comp_scale_offset_bit_depth bits.

The variable CompScaleScaleVal[c][i] is derived as follows:

CompScaleScaleVal[ c ][ i ] = ( comp_scale_scale_val[ c ][ i ] >>comp_scale_scale_frac_bit_depth ) + ( comp_scale_scale_val[ c ][ i ] & ((1 << comp_scale_scale_frac_bit_depth ) − 1 ) ) (1 <<comp_scale_scale_frac_bit_depth )

comp_scale_offset_val[c][i] is used to derive the offset value that isused to derive the width of the of the i-th partition of the c-thcomponent. The length of comp_scale_global_offset_val[c] iscomp_scale_offset_bit_depth bits.

When comp_scale_offset_val[c][i] is signalled, the value ofCompScaleOffsetVal[c][i] is derived as follows:

CompScaleOffsetVal[ c ][ i ] = ( comp_scale_offset_val[ c ][ i ] >>comp_scale_offset_frac_bit_depth ) + ( comp_scale_offset_val[ c ][ i ] &( (1 << comp_scale_offset_frac_bit_depth ) − 1 ) )) ÷ (1 <<comp_scale_offset_frac_bit_depth )

Alternatively, the variable CompScaleScaleVal[c][i] andCompScaleOffsetVal[c][i] are derived as follows:

CompScaleScaleVal[ c ][ i ] = comp_scale_scale_val[ c ][ i ] & (1 <<comp_scale_scale_frac_bit_depth ) CompScaleOffsetVal[ c ][ i ] =comp_scale_offset_val[ c ][ i ] ÷ (1 << comp_scale_offset_frac_bit_depth)

When comp_scale_equal_ranges_flag[c] is equal to 1,comp_scale_offset_val[c][i] is not signalled, and the value ofCompScaleOffsetVal[c][i] is derived as follows:

CompScaleOffsetVal[c][i]=1÷comp_scale_num_ranges[c]

The variable CompScaleOutputRanges[c][i] and CompScaleOutputRanges[c][i]for i in the range of 0 to comp_scale_num_ranges[c] is derived asfollows:

for( i = 0; i <= comp_scale_num_ranges[ c ]; i++ )     if( i == 0 )      CompScaleOutputRanges[ c ][ i ] = comp_scale_global_offset_val[ c]÷                   (1 << comp_scale_offset_frac_bit_depth )      CompScaleInputRanges[ c ][ i ] = 0     else      CompScaleInputRanges[ c ][ i ] = CompScaleOffsetInputRanges[ c ][i − 1 ] +               (CompScaleOffsetVal[ c ][ i − 1 ] *CompScaleScaleVal[ c ][ i − 1 ]       CompScaleOutputRanges[ c ][ i ] =CompScaleOutputRanges[ c ][ i − 1 ] +                  CompScaleOffsetVal[ c ][ i − 1 ]

In one alternative, the values of CompScaleOutputRanges[ ][ ] andCompScaleOutputRanges[ ][ ] are derived as follows:

for( i = 0; i <= comp_scale_num_ranges[ c ]; i++ )     if( i == 0 )      CompScaleInputRanges[ c ][ i ] = comp_scale_global_offset_val[ c]÷                   (1 << comp_scale_offset_frac_bit_depth )      CompScaleOutputRanges[ c ][ i ] = 0     else      CompScaleInputRanges[ c ][ i ] = CompScaleOffsetInputRanges[ c ][i − 1 ] +               (CompScaleOffsetVal[ c ][ i − 1 ] *CompScaleScaleVal[ c ][ i − 1 ]       CompScaleOutputRanges[ c ][ i ] =CompScaleOutputRanges[ c ][ i − 1 ] +               CompScaleOffsetVal[c ][ i − 1 ]

The process of mapping an input signal representation (which may be usedto cover both integer as well as floating point) x and an output signalrepresentation y, where the sample values for both input representationis normalized in the range of 0 to 1, and output representation is inthe range of and 0 to 1, is specified as follows:

if( x <= CompScaleInputRanges[ c ][ 0 ] )   y = CompScaleOutputRanges[ c][ 0 ] else if( x > CompScaleInputRanges[ c ][ comp_scale_num_ranges[ c] ] )   y = CompScaleOutputRanges[ c ][ comp_scale_num_ranges[ c ]; ]else   for( i = 1; i <= comp_scale_num_ranges[ c ]; i++ )     if(CompScaleInputRanges[ i − 1 ] < x && x <= CompScaleInputRanges[ i ] )      y = ( x − CompScaleInputRanges[ i − 1 ] ) □ comp_scale_val[ c ][ i] +         CompScaleOutputRanges[ c ][ i − 1 ]

In one alternative, the value of CompScaleOutputRanges[c][0] is setbased on the permitted sample value range.

Alternatively, the process of mapping an input value valIn to outputvalue valOut is defined as follows:

m_pAtfRangeIn[ 0 ] = 0; m_pAtfRangeOut[ 0 ] = −m_offset2*m_pAtfScale2[c][0]; for (int j = 1; j < m_atfNumberRanges + 1; j++) {m_pAtfRangeIn[ j ] = m_pAtfRangeIn[j − 1] + m_pAtfDelta[j − 1];m_pAtfRangeOut[ j ] = m_pAtfRangeOut[j − 1] + m_pAtfScale2[ c ][ j − 1] * m_pAtfDelta[ j − 1 ]; } for (int j = 0; j < numRanges && skip = = 0;j++) { if (valIn <= pAtfRangeIn[ j + 1 ]) { valOut = (valIn −pOffset[component][ j ]) * pScale[ component ][ j ]; skip = 1; } ]

In one alternative, m_offset2 is equal tocomp_scale_global_offset_val[c]÷(1<<comp_scale_offset_frac_bit_depth),m_pAtfScale[c][i] is equal to CompScaleScaleVal[c][i] and m_pAtfDelta[i]is equal to CompScaleOffsetVal[c][i] for the c-th component, and pScaleand pOffset are scale and offset parameter derived from m_AtfScale andm_pAtfDelta.

An inverse operation would be defined accordingly.

Example 6

In some examples, some of signaling methods described above, e.g. inexample 5, can be utilized as shown in following pseudo code.

m_atfNumberRanges is a term for syntax elements comp_scale_num_ranges[c]for a given c, that specifies number of dynamic range partitioning formapped data.

m_pAtfRangeIn is a term for CompScaleInputRanges, is an arrays size ofm_atfNumberRanges+1 that includes input sample value specifying theborder between two concatenated partitions, e.g., i and i+1.

m_pAtfRangeOut is a term for CompScaleOutputRanges, is an arrays size ofm_atfNumberRanges+1 that includes output sample value specifying theborder between two concatenated partitions, e.g. i and i+1.

m_pAtfScale2 is a term for variable CompScaleScaleVal [c] is an arrayssize of m_atfNumberRanges that includes scale values for eachpartitions.

m_pAtfOffset2 is an array arrays size of m_atfNumberRanges that includesoffset values for each partition.

m_offset2 is a term for comp_scale_global_offset_val.

In this example, parameters of piece-wise linear model can be determinedform syntax elements as in Algorithm 1:

Algorithm 1: m_pAtfRangeIn[0] = 0; m_pAtfRangeOut[0] = −m_offset2*m_pAtfScale2[c][0]; for (int j = 1; j < m_atfNumberRanges + 1; j++) {m_pAtfRangeIn[j] = m_pAtfRangeIn[j − 1] + m_pAtfDelta[j − 1];m_pAtfRangeOut[j] = m_pAtfRangeOut[j − 1] + m_pAtfScale2[c][j − 1] *m_pAtfDelta[j − 1]; } for (int j = 0; j < m_atfNumberRanges; j++) { temp= m_pAtfRangeIn[j + 1] − m_pAtfRangeOut[j + 1] / m_pAtfScale2[c][j];m_pAtfOffset2[c][j] = temp; }

Once determined, piece-wise linear model can be applied to input samplesvalue inValue to determine output sample value outValue as in Algorithm2:

Algorithm 2: for (int j = 0; j < m_atfNumberRanges && skip == 0; j++) {if (inValue <= m_pAtfRangeIn[j + 1]) { outvalue = (inValue −m_pAtfOffset2 [j]) * m_pAtfScale2 [j]; skip = 1; } } Inverse process tobe conducted as in Algorithm 3: Algorithm 3: for (int j = 0; j <m_atfNumberRanges && skip == 0; j++) { if (inValue <= m_pAtfRangeOut[j +1]) { outValue = inValue / m_pAtfScale2 [j] + m_pAtfOffset2 [j]; skip =1; } }

In some examples, border sample value (an entry of m_pAtfRangeIn orm_pAtfRangeOut) between two concatenated partitions i and i+1 can beinterpreted differently, as belonging to i+1, instead of belonging to ipartition as it is shown in Algorithm 2 and 3.

In some examples, inverse process shown in Algorithm 3, can beimplemented with a multiplication by m_pAtfInverseScale2 value, insteadof division by m_pAtfScale2[j]. In such examples, a value ofm_pAtfScale2[j] is determined from m_pAtfScale2[j] in advance.

In some examples, m_pAtfInverseScale2[j] is determined at the decoderside as 1/m_pAtfScale2[j].

In some examples, m_pAtfInverseScale2[j] can be computed at the encoderside, and signalled through bitstream. In such examples, operation givenin Algorithms 1, 2 and 3 will be adjusted accordingly.

VARIOUS EXAMPLES

In some examples, proposed signaling mechanism can be used to model apiece-wise function that can be utilized to enable dynamical rangeadjustment for samples of input signal, e.g. to improve compressionefficiency of video coding systems.

In some examples, proposed signaling mechanism can be used to model apiece-wise function that can be applied to codewords (non-linearrepresentation of R,G,B samples) produced by an OETF, e.g. by PQ TF ofST.2084, or others.

In some examples, proposed signaling mechanism can be used to model apiece-wise function that can be applied to samples of YCbCr colorrepresentation.

In some examples, proposed signaling mechanism can be used to model apiece-wise function that can be utilized to HDR/WCG solutions with SDRcompatibility.

In some examples, proposed signaling mechanism can be used to model apiece-wise function that can be applied to samples in floating pointrepresentation. In yet another example, proposed signaling mechanism andresulting function can be applied to samples in integer representation,e.g. 10 bits.

In some examples, proposed signaling mechanism can be used to model apiece-wise function that can be applied to samples in a form of Look UpTables. In yet another examples, proposed signaling can be used to modelfunction that can be applied to a sample in a form of multiplier.

Combinations and Extensions

In the examples above, a linear model is assumed for each region (i.e.,scale plus offset); the techniques of this disclosure also may beapplicable for higher-order polynomial models, for example, with apolynomial of 2nd degree requiring three parameters instead of two. Thesignaling and syntax would be properly extended for this scenario.

Combinations of aspects described above are possible and part of thetechniques of this disclosure.

Toolbox combination: there are several HDR methods that can targetsomewhat similar goals to those of the SEIs described in thisdisclosure. In order to accommodate more than one of them but, at thesame time, limiting the number of applicable SEI processing per frame,it is proposed to combine (one or more of) these methods in a singleSEI. A proposed syntax element would indicate the specific method toapply in each instance. For example, if there are two possible methodsin the SEI, the syntax element would be a flag indicating the one to beused.

Example 7

In this example, the signaling of scale parameters is modified such thatnegative scales can be transmitted, and the signaled scale parametersindicate the variation of scale to be applied for different ranges ofthe various components. The changes with respect to example 5 are below.

Changes to Syntax of the SEI Message

De- scrip- tor component_scale_info( payloadSize ) { comp_scale_id ue(v)comp_scale_cancel_flag u(1) if( !comp_scale_cancel_flag ) {comp_scale_persistence_flag u(1) comp_scale_scale_bit_depth u(4)comp_scale_offset_bit_depth u(4) comp_scale_scale_frac_bit_depth u(4)comp_scale_offset_frac_bit_depth u(4)comp_scale_negative_scales_present_flag u(1) comp_scale_dep_component_idue(v) comp_scale_num_comps_minus1 ue(v) for( c = 0; c <=comp_scale_num_comps_minus1; c++ ) { comp_scale_num_ranges[ c ] ue(v)comp_scale_equal_ranges_flag[ c ] u(1) comp_scale_global_offset_val[ c ]u(v) for( i = 0; i <= comp_scale_num_ranges[ c ]; i++ )comp_scale_scale_val[ c ][ i ] u(v) if( !comp_scale_equal_ranges[ c ] )u(v) for( i = 0; i <= comp_scale_num_ranges[ c ]; i++ )comp_scale_offset_val[ c ][ i ] u(v) } }

Changes to Semantics of the SEI Message

comp_scale_negative_scales_present_flag equal to 1 specifies that theinteger part of the scale parameters derived fromcomp_scale_scale_val[c][i] is represented as a signed integer.comp_scale_negative_scales_present flag equal to 0 specifies that theinteger part scale parameters derived from comp_scale_scale_val[c][i] isrepresented as an unsigned integer.

In one alternative, another set of offset parameters are signaled alongwith comp_scale_scale_val that are used to define the offset that isapplied along with the scale on a first component as a function of thevalue of a second component.

The signed-integer representation includes, but is not limited to,twos-complement notation and signed magnitude representation (one bitfor sign and the remaining bits in the integer-part). The derivationbelow is given for the signed magnitude representation. The derivationcan be similarly defined for other forms of signed representations.

The variable CompScaleScaleVal[c][i] is derived as follows:

compScaleScaleFracPart = ( comp_scale_scale_val[ c ][ i ] & ( (1 <<comp_scale_scale_frac_bit_depth ) − 1 ) ) (1 <<comp_scale_scale_frac_bit_depth ) if(comp_scale_negative_scales_present_flag ) {   compScaleSignPart =comp_scale_scale_val[ c ][ i ] >> (comp_scale_scale_bit_depth − 1 )  compScaleIntegerPart = comp_scale_scale_val[ c ][ i ] − (compScaleSignPart << (comp_scale_scale_bit_depth − 1) )  compScaleIntegerVal = ( ( compScaleSignPart = = 1 ) : −1 : 1 ) *compScaleIntegerPart } else   compScaleIntegerVal =comp_scale_scale_val[ c ][ i ] >> comp_scale_scale_frac_bit_depthCompScaleScaleVal[ c ][ i ] = compScaleIntegerVal +compScaleScaleFracPart

It is a requirement of bitstream conformance that when comp_scalenegative_scale_present_flag is equal to 1, the value ofcomp_scale_scale_bit depth shall be greater than or equal tocomp_scale_scale_frac_bit_depth

comp_scale_dependent_component_id specifies the application of scale andoffset parameters to the various components of the video. Whencomp_scale_dependent_component_id is equal to 0, the syntax elementscomp_scale_global_offset_val[c], comp_scale scale_val[c][i] andcomp_scale_offset_val[c][i] are used to identify mapping of input andoutput values of the c-th component. Whencomp_scale_dependent_component_id is greater than 0,comp_scale_dependent_component_id−1 specifies the index of the componentsuch that the syntax elements comp_scale_global_offset_val[c],comp_scale_scale_val[c][i] and comp_scale_offset_val[c][i] specify themapping of a scale parameter to be applied to the c-th component of asample as a function of the value of (comp_scale_dependent_componentid−1)-th component of the sample.

The rest of the semantics are similar to those described in Example 5.

Example 8

In this example, the bit depth of the ATF parameters depend on thecomponent. For each component, the bit depth of the syntax elements isexplicitly signal. In addition, there are default bit-depth for thosesyntax elements. The default value is assigned when the bit depth is notexplicitly signaled. A flag might indicate whether the default valuesare applied or they are explicitly signaled.

The table below shows an example of these concepts. Syntax elements ofthe ATF parameters are the scale hdr_recon_scale_val[ ][ ] and rangehdr_recon_range_val[ ][ ]. The syntax elements indicating thecorresponding bit depth (integer and fractional part) are the followingones:

hdr_recon_scale_bit_depth[c],

hdr_recon_offset_bit_depth[c],

hdr_recon_scale_frac_bit_depth[c],

hdr_recon_offset_frac_bit_depth[c],

where c is the component index. The default bit-depths for scale andoffset (range) can be set to:

hdr_recon_scale_bit_depth[c]=8,

hdr_recon_offset_bit_depth[c]=8,

hdr_recon_scale_frac_bit_depth[c]=6,

hdr_recon_offset_frac_bit_depth[c]=8.

The accuracy of the parameters might also be different for the ATFparameters and the color adjustment parameters. Also, the default mightbe different per component and for the color adjustment parameters. Inthis example, the defaults are assumed to be the same.

Descriptor hdr_reconstruction_info( payloadSize ) { hdr_recon_id ue(v)hdr_recon_cancel_flag u(1) if( !hdr_recon_cancel_flag ) {hdr_recon_persistence_flag u(1) if (hdr_recon_id = = 1 ) {hdr_output_full_range_flag hdr_output_colour_primarieshdr_output_transfer_characteristics hdr_output_matrix_coeffs } SYNTAXFOR THE MAPPING LUTs hdr_recon_num_comps_minus1 ue(v) for( c = 0; c <=hdr_recon_num_comps_minus1; c++ ) {  hdr_recon_default_bit_depth [ c ]u(1)  if ( hdr_recon_default_bit_depth [ c ] == 0) {hdr_recon_scale_bit_depth[ c ] u(4) hdr_recon_offset_bit_depth[ c ] u(4)hdr_recon_scale_frac_bit_depth[ c ] u(4)hdr_recon_offset_frac_bit_depth[ c ] u(4)  } hdr_recon_num_ranges[ c ]ue(v) hdr_recon_equal_ranges_flag[ c ] u(1) hdr_recon_global_offset_val[c ] u(v) for( i = 0; i <= hdr_recon_num_ranges[ c ]; i++ )hdr_recon_scale_val[ c ][ i ] u(v) if( !hdr_recon_equal_ranges[ c ] )u(v) for( i = 0; i <= hdr_recon_num_ranges[ c ]; i++ )hdr_recon_range_val [ c ][ i ] u(v) } u(v) SYNTAX FOR THE COLORCORRECTION PART if (hdr_recon_id = = 1 ) { Params related to Colourcorrection hdr_ color_correction_type 0: on U, V − 1: on R, G, Bhdr_color_accuracy_flag Syntax for coding the colour if( !hdr_recon_color_accuracy_flag ) { correction LUT hdr_color_scale_bit_depth u(4) hdr_color _offset_bit_depth u(4) hdr_color_scale_frac_bit_depth u(4) hdr_color _offset_frac_bit_depth u(4) }color_correction_num_ranges color_correction_equal_len_ranges_flagcolor_correction_zero_offset_val for( i = 0; i <color_correction_num_ranges; i++ ) color_correction_scale_val[ i ] if( !color_correction_equal_len_ranges_flag ) for( i = 0; i <color_correction_num_ranges; i++ ) color_correction_range_val[ i ] } } }}

Example 9

A desirable property of a new HDR solution is that it is backwardcompatible to previous HDR solutions, like HDR10. A syntax element mayindicate that this is the case. This indicates a characteristic of thebitstream, and an HDR decoder might decide not to spend computationalresources on the inverse ATF processing under some circumstances if thenon ATF version is already viewable.

In one example, some values of the hdr_recon_id syntax element arereserved to indicate HDR10 backward compatibility, or to what degreethere is backward compatibility.

In another example, a flag (hdr_recon_hdr10_bc) indicates thissituation.

In one example, the signaled HDR10 backward compatibility indicates thatthe bitstream is viewable. Alternatively, it might indicate somespecific properties of the signaled values: for example, that they are arange of values that guarantees this property. For instance, aconstraint could be that the scale is between 0.9 and 1.1.

FIG. 10 is a block diagram illustrating an example of video encoder 20that may implement the techniques of this disclosure. Video encoder 20may perform intra- and inter-coding of video blocks within video slicesin a target color container that have been processed by videopre-processor unit 19. Intra-coding relies on spatial prediction toreduce or remove spatial redundancy in video within a given video frameor picture.

Inter-coding relies on temporal prediction to reduce or remove temporalredundancy in video within adjacent frames or pictures of a videosequence. Intra-mode (I mode) may refer to any of several spatial basedcoding modes. Inter-modes, such as uni-directional prediction (P mode)or bi-prediction (B mode), may refer to any of several temporal-basedcoding modes.

As shown in FIG. 10, video encoder 20 receives a current video blockwithin a video frame to be encoded. In the example of FIG. 10, videoencoder 20 includes mode select unit 40, a video data memory 41, decodedpicture buffer 64, summer 50, transform processing unit 52, quantizationunit 54, and entropy encoding unit 56. Mode select unit 40, in turn,includes motion compensation unit 44, motion estimation unit 42, intraprediction processing unit 46, and partition unit 48. For video blockreconstruction, video encoder 20 also includes inverse quantization unit58, inverse transform processing unit 60, and summer 62. A deblockingfilter (not shown in FIG. 10) may also be included to filter blockboundaries to remove blockiness artifacts from reconstructed video. Ifdesired, the deblocking filter would typically filter the output ofsummer 62. Additional filters (in loop or post loop) may also be used inaddition to the deblocking filter. Such filters are not shown forbrevity, but if desired, may filter the output of summer 50 (as anin-loop filter).

Video data memory 41 may store video data to be encoded by thecomponents of video encoder 20. The video data stored in video datamemory 41 may be obtained, for example, from video source 18. Decodedpicture buffer 64 may be a reference picture memory that storesreference video data for use in encoding video data by video encoder 20,e.g., in intra- or inter-coding modes. Video data memory 41 and decodedpicture buffer 64 may be formed by any of a variety of memory devices,such as dynamic random access memory (DRAM), including synchronous DRAM(SDRAM), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or othertypes of memory devices. Video data memory 41 and decoded picture buffer64 may be provided by the same memory device or separate memory devices.In various examples, video data memory 41 may be on-chip with othercomponents of video encoder 20, or off-chip relative to thosecomponents.

During the encoding process, video encoder 20 receives a video frame orslice to be coded. The frame or slice may be divided into multiple videoblocks. Motion estimation unit 42 and motion compensation unit 44perform inter-predictive coding of the received video block relative toone or more blocks in one or more reference frames to provide temporalprediction. Intra prediction processing unit 46 may alternativelyperform intra-predictive coding of the received video block relative toone or more neighboring blocks in the same frame or slice as the blockto be coded to provide spatial prediction. Video encoder 20 may performmultiple coding passes, e.g., to select an appropriate coding mode foreach block of video data.

Moreover, partition unit 48 may partition blocks of video data intosub-blocks, based on evaluation of previous partitioning schemes inprevious coding passes. For example, partition unit 48 may initiallypartition a frame or slice into LCUs, and partition each of the LCUsinto sub-CUs based on rate-distortion analysis (e.g., rate-distortionoptimization). Mode select unit 40 may further produce a quadtree datastructure indicative of partitioning of an LCU into sub-CUs. Leaf-nodeCUs of the quadtree may include one or more PUs and one or more TUs.

Mode select unit 40 may select one of the coding modes, intra or inter,e.g., based on error results, and provides the resulting intra- orinter-coded block to summer 50 to generate residual block data and tosummer 62 to reconstruct the encoded block for use as a reference frame.Mode select unit 40 also provides syntax elements, such as motionvectors, intra-mode indicators, partition information, and other suchsyntax information, to entropy encoding unit 56.

Motion estimation unit 42 and motion compensation unit 44 may be highlyintegrated, but are illustrated separately for conceptual purposes.Motion estimation, performed by motion estimation unit 42, is theprocess of generating motion vectors, which estimate motion for videoblocks. A motion vector, for example, may indicate the displacement of aPU of a video block within a current video frame or picture relative toa predictive block within a reference picture (or other coded unit)relative to the current block being coded within the current picture (orother coded unit). A predictive block is a block that is found toclosely match the block to be coded, in terms of pixel difference, whichmay be determined by sum of absolute difference (SAD), sum of squaredifference (SSD), or other difference metrics. In some examples, videoencoder 20 may calculate values for sub-integer pixel positions ofreference pictures stored in decoded picture buffer 64. For example,video encoder 20 may interpolate values of one-quarter pixel positions,one-eighth pixel positions, or other fractional pixel positions of thereference picture. Therefore, motion estimation unit 42 may perform amotion search relative to the full pixel positions and fractional pixelpositions and output a motion vector with fractional pixel precision.

Motion estimation unit 42 calculates a motion vector for a PU of a videoblock in an inter-coded slice by comparing the position of the PU to theposition of a predictive block of a reference picture. The referencepicture may be selected from a first reference picture list (List 0) ora second reference picture list (List 1), each of which identify one ormore reference pictures stored in decoded picture buffer 64. Motionestimation unit 42 sends the calculated motion vector to entropyencoding unit 56 and motion compensation unit 44.

Motion compensation, performed by motion compensation unit 44, mayinvolve fetching or generating the predictive block based on the motionvector determined by motion estimation unit 42. Again, motion estimationunit 42 and motion compensation unit 44 may be functionally integrated,in some examples. Upon receiving the motion vector for the PU of thecurrent video block, motion compensation unit 44 may locate thepredictive block to which the motion vector points in one of thereference picture lists. Summer 50 forms a residual video block bysubtracting pixel values of the predictive block from the pixel valuesof the current video block being coded, forming pixel difference values,as discussed below. In general, motion estimation unit 42 performsmotion estimation relative to luma components, and motion compensationunit 44 uses motion vectors calculated based on the luma components forboth chroma components and luma components. Mode select unit 40 may alsogenerate syntax elements associated with the video blocks and the videoslice for use by video decoder 30 in decoding the video blocks of thevideo slice.

Intra prediction processing unit 46 may intra-predict a current block,as an alternative to the inter-prediction performed by motion estimationunit 42 and motion compensation unit 44, as described above. Inparticular, intra prediction processing unit 46 may determine anintra-prediction mode to use to encode a current block. In someexamples, intra prediction processing unit 46 may encode a current blockusing various intra-prediction modes, e.g., during separate encodingpasses, and intra prediction processing unit 46 (or mode select unit 40,in some examples) may select an appropriate intra-prediction mode to usefrom the tested modes.

For example, intra prediction processing unit 46 may calculaterate-distortion values using a rate-distortion analysis for the varioustested intra-prediction modes, and select the intra-prediction modehaving the best rate-distortion characteristics among the tested modes.Rate-distortion analysis generally determines an amount of distortion(or error) between an encoded block and an original, unencoded blockthat was encoded to produce the encoded block, as well as a bit rate(that is, a number of bits) used to produce the encoded block. Intraprediction processing unit 46 may calculate ratios from the distortionsand rates for the various encoded blocks to determine whichintra-prediction mode exhibits the best rate-distortion value for theblock.

After selecting an intra-prediction mode for a block, intra predictionprocessing unit 46 may provide information indicative of the selectedintra-prediction mode for the block to entropy encoding unit 56. Entropyencoding unit 56 may encode the information indicating the selectedintra-prediction mode. Video encoder 20 may include in the transmittedbitstream configuration data, which may include a plurality ofintra-prediction mode index tables and a plurality of modifiedintra-prediction mode index tables (also referred to as codeword mappingtables), definitions of encoding contexts for various blocks, andindications of a most probable intra-prediction mode, anintra-prediction mode index table, and a modified intra-prediction modeindex table to use for each of the contexts.

Video encoder 20 forms a residual video block by subtracting theprediction data from mode select unit 40 from the original video blockbeing coded. Summer 50 represents the component or components thatperform this subtraction operation. Transform processing unit 52 appliesa transform, such as a discrete cosine transform (DCT) or a conceptuallysimilar transform, to the residual block, producing a video blockcomprising residual transform coefficient values. Transform processingunit 52 may perform other transforms which are conceptually similar toDCT. Wavelet transforms, integer transforms, sub-band transforms orother types of transforms could also be used. In any case, transformprocessing unit 52 applies the transform to the residual block,producing a block of residual transform coefficients. The transform mayconvert the residual information from a pixel value domain to atransform domain, such as a frequency domain. Transform processing unit52 may send the resulting transform coefficients to quantization unit54.

Quantization unit 54 quantizes the transform coefficients to furtherreduce bit rate. The quantization process may reduce the bit depthassociated with some or all of the coefficients. The degree ofquantization may be modified by adjusting a quantization parameter. Insome examples, quantization unit 54 may then perform a scan of thematrix including the quantized transform coefficients. Alternatively,entropy encoding unit 56 may perform the scan.

Following quantization, entropy encoding unit 56 entropy codes thequantized transform coefficients. For example, entropy encoding unit 56may perform context adaptive variable length coding (CAVLC), contextadaptive binary arithmetic coding (CABAC), syntax-based context-adaptivebinary arithmetic coding (SBAC), probability interval partitioningentropy (PIPE) coding or another entropy coding technique. In the caseof context-based entropy coding, context may be based on neighboringblocks. Following the entropy coding by entropy encoding unit 56, theencoded bitstream may be transmitted to another device (e.g., videodecoder 30) or archived for later transmission or retrieval.

Inverse quantization unit 58 and inverse transform processing unit 60apply inverse quantization and inverse transformation, respectively, toreconstruct the residual block in the pixel domain, e.g., for later useas a reference block. Motion compensation unit 44 may calculate areference block by adding the residual block to a predictive block ofone of the frames of decoded picture buffer 64. Motion compensation unit44 may also apply one or more interpolation filters to the reconstructedresidual block to calculate sub-integer pixel values for use in motionestimation. Summer 62 adds the reconstructed residual block to themotion compensated prediction block produced by motion compensation unit44 to produce a reconstructed video block for storage in decoded picturebuffer 64. The reconstructed video block may be used by motionestimation unit 42 and motion compensation unit 44 as a reference blockto inter-code a block in a subsequent video frame.

FIG. 11 is a block diagram illustrating an example of video decoder 30that may implement the techniques of this disclosure. In particular,video decoder 30 may decode video data into a target color containerthat may then be processed by video post-processor unit 31, as describedabove. In the example of FIG. 11, video decoder 30 includes an entropydecoding unit 70, a video data memory 71, motion compensation unit 72,intra prediction processing unit 74, inverse quantization unit 76,inverse transform processing unit 78, decoded picture buffer 82 andsummer 80. Video decoder 30 may, in some examples, perform a decodingpass generally reciprocal to the encoding pass described with respect tovideo encoder 20 (FIG. 10). Motion compensation unit 72 may generateprediction data based on motion vectors received from entropy decodingunit 70, while intra prediction processing unit 74 may generateprediction data based on intra-prediction mode indicators received fromentropy decoding unit 70.

Video data memory 71 may store video data, such as an encoded videobitstream, to be decoded by the components of video decoder 30. Thevideo data stored in video data memory 71 may be obtained, for example,from computer-readable medium 16, e.g., from a local video source, suchas a camera, via wired or wireless network communication of video data,or by accessing physical data storage media. Video data memory 71 mayform a coded picture buffer (CPB) that stores encoded video data from anencoded video bitstream. Decoded picture buffer 82 may be a referencepicture memory that stores reference video data for use in decodingvideo data by video decoder 30, e.g., in intra- or inter-coding modes.Video data memory 71 and decoded picture buffer 82 may be formed by anyof a variety of memory devices, such as dynamic random access memory(DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM),resistive RAM (RRAM), or other types of memory devices. Video datamemory 71 and decoded picture buffer 82 may be provided by the samememory device or separate memory devices. In various examples, videodata memory 71 may be on-chip with other components of video decoder 30,or off-chip relative to those components.

During the decoding process, video decoder 30 receives an encoded videobitstream that represents video blocks of an encoded video slice andassociated syntax elements from video encoder 20. Entropy decoding unit70 of video decoder 30 entropy decodes the bitstream to generatequantized coefficients, motion vectors or intra-prediction modeindicators, and other syntax elements. Entropy decoding unit 70 forwardsthe motion vectors to and other syntax elements to motion compensationunit 72. Video decoder 30 may receive the syntax elements at the videoslice level and/or the video block level.

When the video slice is coded as an intra-coded (I) slice, intraprediction processing unit 74 may generate prediction data for a videoblock of the current video slice based on a signaled intra predictionmode and data from previously decoded blocks of the current frame orpicture. When the video frame is coded as an inter-coded (i.e., B or P)slice, motion compensation unit 72 produces predictive blocks for avideo block of the current video slice based on the motion vectors andother syntax elements received from entropy decoding unit 70. Thepredictive blocks may be produced from one of the reference pictureswithin one of the reference picture lists. Video decoder 30 mayconstruct the reference picture lists, List 0 and List 1, using defaultconstruction techniques based on reference pictures stored in decodedpicture buffer 82. Motion compensation unit 72 determines predictioninformation for a video block of the current video slice by parsing themotion vectors and other syntax elements, and uses the predictioninformation to produce the predictive blocks for the current video blockbeing decoded. For example, motion compensation unit 72 uses some of thereceived syntax elements to determine a prediction mode (e.g., intra- orinter-prediction) used to code the video blocks of the video slice, aninter-prediction slice type (e.g., B slice or P slice), constructioninformation for one or more of the reference picture lists for theslice, motion vectors for each inter-encoded video block of the slice,inter-prediction status for each inter-coded video block of the slice,and other information to decode the video blocks in the current videoslice.

Motion compensation unit 72 may also perform interpolation based oninterpolation filters. Motion compensation unit 72 may use interpolationfilters as used by video encoder 20 during encoding of the video blocksto calculate interpolated values for sub-integer pixels of referenceblocks. In this case, motion compensation unit 72 may determine theinterpolation filters used by video encoder 20 from the received syntaxelements and use the interpolation filters to produce predictive blocks.

Inverse quantization unit 76 inverse quantizes, i.e., de-quantizes, thequantized transform coefficients provided in the bitstream and decodedby entropy decoding unit 70. The inverse quantization process mayinclude use of a quantization parameter QPY calculated by video decoder30 for each video block in the video slice to determine a degree ofquantization and, likewise, a degree of inverse quantization that shouldbe applied. Inverse transform processing unit 78 applies an inversetransform, e.g., an inverse DCT, an inverse integer transform, or aconceptually similar inverse transform process, to the transformcoefficients in order to produce residual blocks in the pixel domain.

After motion compensation unit 72 generates the predictive block for thecurrent video block based on the motion vectors and other syntaxelements, video decoder 30 forms a decoded video block by summing theresidual blocks from inverse transform processing unit 78 with thecorresponding predictive blocks generated by motion compensation unit72. Summer 80 represents the component or components that perform thissummation operation. If desired, a deblocking filter may also be appliedto filter the decoded blocks in order to remove blockiness artifacts.Other loop filters (either in the coding loop or after the coding loop)may also be used to smooth pixel transitions, or otherwise improve thevideo quality. The decoded video blocks in a given frame or picture arethen stored in decoded picture buffer 82, which stores referencepictures used for subsequent motion compensation. Decoded picture buffer82 also stores decoded video for later presentation on a display device,such as display device 32 of FIG. 1.

FIG. 12 is a flowchart showing one example video processing technique ofthe disclosure. The techniques of FIG. 12 may be performed by videoencoder 20 and/or video pre-processor unit 19. In the example of FIG.12, source device 12 may be configured to capture video data using acamera (1200). Video encoder 20 and/or video pre-processor unit 19 maybe configured to perform a dynamic range adjustment process on videodata using fixed-point computing (1210). Video encoder 20 and/or videopre-processor unit 19 may be further configured to generate one or moresyntax elements that contain information specifying how to determineparameters for performing an inverse dynamic range adjustment process,relative to the dynamic range adjustment process, using fixed-pointcomputing (1220).

In one example, video encoder 20 and/or video pre-processor unit 19 maybe configured to generate the one or more syntax elements by generatingthe one or more syntax elements in one or more supplemental enhancementinformation (SEI) messages. In one example, the parameters comprise oneor more of a range parameter, a scale parameter, or an offset parameter.In another example, the information indicates one or more of a firstnumber of fractional bits used for determining the range parameter, asecond number of fractional bits used for determining the scaleparameter, and a third number of fractional bits used for determiningthe offset parameter. In another example, the information includes aminimum value and a maximum value for one or more color components ofthe video data. In another example, the information includes an index toa predetermined range of sample values of the decoded video data.

FIG. 13 is a flowchart showing another example video processingtechnique of the disclosure. The techniques of FIG. 13 may be performedby video decoder 30 and/or video post-processor unit 31. In one exampleof the disclosure, video decoder 30 and/or video post-processor unit 31may be configured to receive one or more syntax elements that containinformation specifying how to determine parameters for performing aninverse dynamic range adjustment process (1300), and receive decodedvideo data (1310).

Video decoder 30 and/or video post-processor unit 31 may be furtherconfigured to determine parameters for an inverse dynamic rangeadjustment process from the received information (1320), and perform theinverse dynamic range adjustment process on the decoded video data usingfixed-point computing in accordance with the information received andthe determined parameters (1330). Destination device 14 may be furtherconfigured to display the decoded video data after performing theinverse dynamic range adjustment process on the decoded video data(1340).

In one example of the disclosure, video decoder 30 and/or videopost-processor unit 31 may be configured to receive the one or moresyntax elements in one or more supplemental enhancement information(SEI) messages. In one example, the parameters comprise one or more of arange parameter, a scale parameter, or an offset parameter. In anotherexample, the information indicates one or more of a first number offractional bits used for determining the range parameter, a secondnumber of fractional bits used for determining the scale parameter, anda third number of fractional bits used for determining the offsetparameter.

In another example of the disclosure, video decoder 30 and/or videopost-processor unit 31 may be configured to determine the parameters, inthe case that at least one of the first number of fractional bits, thesecond number of fractional bits, or the third number of fractional bitsis different from one another, by accumulating any fractional bitsduring any intermediate calculation processes used to determine theparameters, and clip a final result for determining the parameters basedon a predetermined fractional accuracy.

In another example of the disclosure, video decoder 30 and/or videopost-processor unit 31 may be configured to determine the parameters bytruncating any fractional bits over a desired fractional accuracy duringall intermediate calculation processes used to determine the parameters.

In another example, the information includes a minimum value and amaximum value for one or more color components of the decoded videodata, and video decoder 30 and/or video post-processor unit 31 may beconfigured to determine the parameters based on the received minimumvalue and the received maximum value.

In another example, the information includes an index to a predeterminedrange of sample values for one or more color components of the decodedvideo data, and video decoder 30 and/or video post-processor unit 31 maybe configured to determine a minimum value and a maximum value for theone or more color components of the decoded video data based on thereceived index, and determine the parameters based on the determinedminimum value and the determined maximum value.

In another example of the disclosure, video decoder 30 and/or videopost-processor unit 31 may be configured to receive a syntax elementindicating if the parameters are signed or unsigned, and perform aparsing process on the information in the SEI message, wherein theparsing process is the same regardless of the value of the syntaxelement.

Certain aspects of this disclosure have been described with respect toextensions of the HEVC standard for purposes of illustration. However,the techniques described in this disclosure may be useful for othervideo coding processes, including other standard or proprietary videocoding processes not yet developed.

A video coder, as described in this disclosure, may refer to a videoencoder or a video decoder. Similarly, a video coding unit may refer toa video encoder or a video decoder. Likewise, video coding may refer tovideo encoding or video decoding, as applicable.

It is to be recognized that depending on the example, certain acts orevents of any of the techniques described herein can be performed in adifferent sequence, may be added, merged, or left out altogether (e.g.,not all described acts or events are necessary for the practice of thetechniques). Moreover, in certain examples, acts or events may beperformed concurrently, e.g., through multi-threaded processing,interrupt processing, or multiple processors, rather than sequentially.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium and executedby a hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablelogic arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor,” as used herein may referto any of the foregoing structure or any other structure suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated hardware and/or software modules configured for encoding anddecoding, or incorporated in a combined codec. Also, the techniquescould be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. A method of processing video data, the methodcomprising: receiving one or more syntax elements that containinformation specifying how to determine one or more parameters forperforming an inverse dynamic range adjustment process, wherein the oneor more parameters comprise one or more of a range parameter, a scaleparameter, or an offset parameter, wherein receiving the one or moresyntax elements comprises receiving the one or more syntax elements inone or more supplemental enhancement information (SEI) messages, andwherein the information includes a minimum value and a maximum value forone or more color components; determining the one or more parametersbased on the minimum value and the maximum value for the one or morecolor components; decoding video data; and performing the inversedynamic range adjustment process on the decoded video data usingfixed-point computing in accordance with the one or more parameters. 2.The method of claim 1, wherein the information further indicates one ormore of a first number of fractional bits used for determining the rangeparameter, a second number of fractional bits used for determining thescale parameter, and a third number of fractional bits used fordetermining the offset parameter.
 3. The method of claim 2, furthercomprising: determining the one or more parameters using the firstnumber of fractional bits, the second number of fractional bits, and thethird number of fractional bits.
 4. The method of claim 3, whereindetermining the one or more parameters further comprises: determiningthe one or more parameters, in the case that at least two of the firstnumber of fractional bits, the second number of fractional bits, or thethird number of fractional bits is different from one another, byaccumulating any fractional bits during any intermediate calculationprocesses used to determine the one or more parameters; and clipping afinal result for determining the one or more parameters based on apredetermined fractional accuracy.
 5. The method of claim 4, whereindetermining the one or more parameters further comprises: truncating anyfractional bits over a desired fractional accuracy during all of theintermediate calculation processes used to determine the one or moreparameters.
 6. The method of claim 1, wherein the information includesan index to a predetermined range of sample values for the one or morecolor components of the decoded video data, the method furthercomprising: determining the minimum value and the maximum value for theone or more color components of the decoded video data based on theindex; and determining the one or more parameters based on thedetermined minimum value and the determined maximum value.
 7. The methodof claim 1, further comprising: receiving a syntax element indicating ifthe one or more parameters are signed or unsigned; and performing aparsing process on the information in the SEI message, wherein theparsing process is the same regardless of the value of the syntaxelement.
 8. The method of claim 1, further comprising: displaying thedecoded video data after performing the inverse dynamic range adjustmentprocess on the decoded video data.
 9. An apparatus configured to processvideo data, the apparatus comprising: a memory configured to storedecoded video data; and one or more processors configured to: receiveone or more syntax elements that contain information specifying how todetermine one or more parameters for performing an inverse dynamic rangeadjustment process, wherein the one or more parameters comprise one ormore of a range parameter, a scale parameter, or an offset parameter,wherein receiving the one or more syntax elements comprises receivingthe one or more syntax elements in one or more supplemental enhancementinformation (SEI) messages, and wherein the information includes aminimum value and a maximum value for one or more color components;determine the one or more parameters based on the minimum value and themaximum value for the one or more color components; decode video data;and perform the inverse dynamic range adjustment process on the decodedvideo data using fixed-point computing in accordance with the one ormore parameters.
 10. The apparatus of claim 9, wherein the informationfurther indicates one or more of a first number of fractional bits usedfor determining the range parameter, a second number of fractional bitsused for determining the scale parameter, and a third number offractional bits used for determining the offset parameter.
 11. Theapparatus of claim 10, wherein the one or more processors are furtherconfigured to: determine the one or more parameters using the firstnumber of fractional bits, the second number of fractional bits, and thethird number of fractional bits.
 12. The apparatus of claim 11, whereinto determine the one or more parameters further, the one or moreprocessors are further configured to: determine the one or moreparameters, in the case that at least two of the first number offractional bits, the second number of fractional bits, or the thirdnumber of fractional bits is different from one another, by accumulatingany fractional bits during any intermediate calculation processes usedto determine the one or more parameters; and clip a final result fordetermining the one or more parameters based on a predeterminedfractional accuracy.
 13. The apparatus of claim 12, wherein to determinethe one or more parameters further, the one or more processors arefurther configured to: truncate any fractional bits over a desiredfractional accuracy during all of the intermediate calculation processesused to determine the one or more parameters.
 14. The apparatus of claim9, wherein the information includes an index to a predetermined range ofsample values for the one or more color components of the decoded videodata, and wherein the one or more processors are further configured to:determine the minimum value and the maximum value for the one or morecolor components of the decoded video data based on the index; anddetermine the one or more parameters based on the determined minimumvalue and the determined maximum value.
 15. The apparatus of claim 9,wherein the one or more processors are further configured to: receive asyntax element indicating if the one or more parameters are signed orunsigned; and perform a parsing process on the information in the SEImessage, wherein the parsing process is the same regardless of the valueof the syntax element.
 16. The apparatus of claim 9, the apparatusfurther comprising: a display configured to display the decoded videodata after the one or more processors perform the inverse dynamic rangeadjustment process on the decoded video data.
 17. The apparatus of claim9, wherein the apparatus comprises one or more of a camera, a computer,a mobile device, a broadcast receiver device, or a set-top box.
 18. Amethod of processing video data, the method comprising: determining oneor more parameters for a dynamic range adjustment process using aminimum value and a maximum value for one or more color components,wherein the one or more parameters include one or more of a rangeparameter, a scale parameter, or an offset parameter; performing thedynamic range adjustment process on video data using the determined oneor more parameters and fixed-point computing; generating one or moresyntax elements that contain information specifying how to determine theone or more parameters for performing an inverse dynamic rangeadjustment process, relative to the dynamic range adjustment process,using fixed-point computing, wherein the information indicates theminimum value and the maximum value for the one or more colorcomponents, and wherein generating the one or more syntax elementscomprises generating the one or more syntax elements in one or moresupplemental enhancement information (SEI) messages; and encoding thevideo data after performing the dynamic range adjustment process. 19.The method of claim 18, wherein the information further indicates one ormore of a first number of fractional bits used for determining the rangeparameter, a second number of fractional bits used for determining thescale parameter, and a third number of fractional bits used fordetermining the offset parameter.
 20. The method of claim 18, whereinthe information further includes an index to a predetermined range ofsample values of the decoded video data.
 21. The method of claim 18,further comprising: capturing the video data with a camera.
 22. Anapparatus configured to process video data, the apparatus comprising: amemory configured to store video data; and one or more processorsconfigured to: determine one or more parameters for a dynamic rangeadjustment process using a minimum value and a maximum value for one ormore color components, wherein the one or more parameters include one ormore of a range parameter, a scale parameter, or an offset parameter;perform the dynamic range adjustment process on video data using thedetermined one or more parameters and fixed-point computing; generateone or more syntax elements that contain information specifying how todetermine the one or more parameters for performing an inverse dynamicrange adjustment process, relative to the dynamic range adjustmentprocess, using fixed-point computing, wherein the information indicatesthe minimum value and the maximum value for the one or more colorcomponents, and wherein generating the one or more syntax elementscomprises generating the one or more syntax elements in one or moresupplemental enhancement information (SEI) messages; and encode thevideo data after performing the dynamic range adjustment process. 23.The apparatus of claim 22, wherein the information further indicates oneor more of a first number of fractional bits used for determining therange parameter, a second number of fractional bits used for determiningthe scale parameter, and a third number of fractional bits used fordetermining the offset parameter.
 24. The apparatus of claim 22, whereinthe information further includes an index to a predetermined range ofsample values of the decoded video data.
 25. The apparatus of claim 22,further comprising: a camera configured to capture the video data. 26.The apparatus of claim 22, wherein the apparatus comprises one or moreof a camera, a computer, a mobile device, a broadcast receiver device,or a set-top box.